Display device and method for driving same

ABSTRACT

Provided is a driving method whereby it is possible to simultaneously compensate for both degradation of a drive transistor and degradation of a light-emitting element without causing special light emission at the time of detecting characteristics in a display device. In a display device which includes a pixel circuit including an electro-optic element and a drive transistor, a driving method includes: a first characteristic detection step for detecting a characteristic of the drive transistor; a second characteristic detection step for detecting a characteristic of the electro-optic element; a correction data storage step for storing characteristic data obtained based on detection results in the first and second characteristic detection steps as correction data; and a video signal correction step for correcting the video signal based on the correction data. The second characteristic detection step is performed in a light emission period.

TECHNICAL FIELD

The present invention relates to a display device and a method fordriving the same, and more specifically to a display device providedwith a pixel circuit including an electro-optic element such as anorganic EL (Electra Luminescence) element, and a method for driving thesame.

BACKGROUND ART

As a display element provided in a display device, there have hithertobeen an electro-optic element whose luminance is controlled by anapplied voltage, and an electro-optic element whose luminance iscontrolled by a flowing current. Examples of the electro-optic elementwhose luminance is controlled by an applied voltage include a liquidcrystal display element. Meanwhile, examples of the electro-opticelement whose luminance is controlled by a flowing current include anorganic EL element. The organic EL element is also called an OLED(Organic Light-Emitting Diode). An organic EL display device that usesthe organic EL element being a spontaneous electro-optic element can beeasily reduced in thickness and power consumption and increased inluminance as compared to the liquid crystal display device that requiresa backlight, a color filter and the like. Hence in recent years,development of the organic EL display device has been actively advanced.

As drive systems for the organic EL display device, a passive matrixsystem (also called simple matrix system) and an active matrix systemare known. As for an organic EL display device employing the passivematrix system, its structure is simple, but a large size and highdefinition are difficult to achieve. In contrast, as for an organic ELdisplay device employing the active matrix system (hereinafter referredto as an “active matrix-type organic EL display device”), a large sizeand high definition can be easily realized as compared to the organic ELdisplay device employing the passive matrix system.

In the active matrix-type organic EL display device, a plurality ofpixel circuits are formed in a matrix form. The pixel circuit of theactive matrix-type organic EL display device typically includes an inputtransistor for selecting a pixel and a drive transistor for controllingsupply of a current to the organic EL element. It is to be noted that inthe following, a current that flows from the drive transistor to theorganic EL element may be referred to as a “drive current”.

FIG. 44 is a circuit diagram showing a configuration of a conventionalgeneral pixel circuit 91. This pixel circuit 91 is providedcorresponding to each of intersections of a plurality of data lines Sand a plurality of scanning lines G which are disposed in a displayportion. As shown in FIG. 44, this pixel circuit 91 is provided with twotransistors T1 and T2, one capacitor Cst, and one organic EL elementOLED. The transistor T1 is an input transistor, and the transistor T2 isa drive transistor.

The transistor T1 is provided between the data line S and a gateterminal of the transistor T2. As for the transistor T1, a gate terminalis connected to the scanning line G, and a source terminal is connectedto the data line S. The transistor T2 is provided in series with theorganic EL element OLED. As for the transistor T2, a drain terminal isconnected to a power supply line that supplies a high-level power supplyvoltage ELVDD, and a source terminal is connected to an anode terminalof the organic EL element OLED. It should be noted that, the powersupply line that supplies the high-level power supply voltage ELVDD isreferred to as a “high-level power supply line” in the following, andthe high-level power supply line is added with the same symbol ELVDD asthat of the high-level power supply voltage. As for the capacitor Cst,one end is connected to the gate terminal of the transistor T2, and theother end is connected to the source terminal of the transistor T2. Acathode terminal of the organic EL element OLED is connected to a powersupply line that supplies a low-level power supply voltage ELVSS. Itshould be noted that, the power supply line that supplies the low-levelpower supply voltage ELVSS is referred to as a “low-level power supplyline” in the following, and the low-level power supply line is addedwith the same symbol ELVSS as that of the low-level power supplyvoltage. Further, here, a contact point of the gate terminal of thetransistor T2, the one end of the capacitor Cst, and the drain terminalof the transistor T1 is referred to as a “gate node VG” for the sake ofconvenience. It is to be noted that, although one having a higherpotential between a drain and a source is generally called a drain, indescriptions of the present specification, one is defined as a drain andthe other is defined as a source, and hence a source potential maybecome higher than a drain potential.

FIG. 45 is a timing chart for explaining an operation of the pixelcircuit 91 shown in FIG. 44. Before time t1, the scanning line G is in anon-selected state. Therefore, before the time t1, the transistor T1 isin an off-state, and a potential of the gate node VG is held at aninitialization level (e.g., a level in accordance with writing in thelast frame). At the time t1, the scanning line G comes into a selectedstate and the transistor T1 is turned on. Thereby, a data voltage Vdatacorresponding to a luminance of a pixel (sub-pixel) formed by this pixelcircuit 91 is supplied to the gate node VG via the data line S and thetransistor T1. Thereafter, in a period till time t2, the potential ofthe gate node VG changes in accordance with the data voltage Vdata. Atthis time, the capacitor Cst is charged with a gate-source voltage Vgswhich is a difference between the potential of the gate node VG and asource potential of the transistor T2. At the time t2, the scanning lineG comes into the non-selected state. Thereby, the transistor T1 isturned off and the gate-source voltage Vgs held by the capacitor Cst isdetermined. The transistor T2 supplies a drive current to the organic ELelement OLED in accordance with the gate-source voltage Vgs held by thecapacitor Cst. As a result, the organic EL element OLED emits light witha luminance in accordance with the drive current.

Incidentally, in the organic EL display device, a thin film transistor(TFT) is typically employed as the drive transistor. However, regardingthe thin film transistor, variations in threshold voltage tend to occur.When variations in threshold voltage occur in the drive transistorprovided in the display portion, variations in luminance occur, and thedisplay quality thus deteriorates. Accordingly, a technique ofsuppressing deterioration in display quality in the organic EL displaydevice has hitherto been proposed. For example, Japanese PatentApplication Laid-Open No. 2005-31630 discloses a technique ofcompensating for variations in threshold voltage of a drive transistor.Further, Japanese Patent Application Laid-Open No. 2003-195810 andJapanese Patent Application Laid-Open No. 2007-128103 each discloses atechnique of making constant a current flowing from a pixel circuit toan organic EL element OLED. Moreover, Japanese Patent ApplicationLaid-Open No. 2007-233326 discloses a technique of displaying an imagewith a uniform luminance regardless of electron mobility and a thresholdvoltage of a drive transistor.

According to the foregoing prior arts, even when variations in thresholdvoltage occur in the drive transistor provided in the display portion,it is possible to supply a constant current to the organic EL element(light-emitting element) in accordance with a desired luminance (targetluminance). However, as for the organic EL element, current efficiencydecreases with the lapse of time. That is, even when a constant currentis supplied to the organic EL element, the luminance gradually decreaseswith the lapse of time. This results in occurrence of burning.

Thus, unless compensation is performed on degradation of the drivetransistor and degradation of the organic EL element, current decreasedue to the degradation of the drive transistor occurs and luminancedecrease due to the degradation of the organic EL element occurs asshown in FIG. 46. Further, even when compensation is performed on thedegradation of the drive transistor, luminance decrease due to thedegradation of the organic EL element occurs with the lapse of time asshown in FIG. 47. Accordingly, Japanese Translation of PCT InternationalApplication Publication No. 2008-523448 discloses a technique ofcorrecting data based on a characteristic of the organic EL element OLEDin addition to the technique of correcting data based on acharacteristic of the drive transistor.

PRIOR ART DOCUMENTS Patent Documents

[Patent Document 1] Japanese Patent Application Laid-Open No. 2005-31630

[Patent Document 2] Japanese Patent Application Laid-Open No.2003-195810

[Patent Document 3] Japanese Patent Application Laid-Open No.2007-128103

[Patent Document 4] Japanese Patent Application Laid-Open No.2007-233326

[Patent Document 5] Japanese Translation of PCT InternationalApplication Publication No. 2008-523448

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, according to the technique disclosed in Japanese Translation ofPCT International Application Publication No. 2008-523448, it is onlypossible to detect the characteristic of either the drive transistor orthe organic EL element during a selection period. Hence it is notpossible to simultaneously compensate for both the degradation of thedrive transistor and the degradation of the organic EL element. Further,detecting the characteristics of both the drive transistor and theorganic EL element requires the selection period to be made long.Concerning this, in the technique disclosed in Japanese Translation ofPCT International Application Publication No. 2008-523448, when theselection period of a row on which the characteristic is detected ismade long, the length of light emission time varies between the row onwhich the characteristic is detected and a row other than that row, andhence a desired luminance display is not made.

Accordingly, it is an object of the present invention to provide adriving method whereby it is possible to simultaneously compensate forboth degradation of a drive transistor and degradation of alight-emitting element without causing special light emission at thetime of detecting characteristics in a display device.

Means for Solving the Problems

A first aspect of the present invention is directed to a method fordriving a display device having an n-row×m-column (n and m are integersnot smaller than 2) pixel matrix including n×m pixel circuits eachincluding an electro-optic element whose luminance is controlled by acurrent and a drive transistor configured to control a current to besupplied to the electro-optic element, the method comprising:

a first characteristic detection step of detecting a characteristic ofthe drive transistor;

a second characteristic detection step of detecting a characteristic ofthe electro-optic element;

a correction data storage step of storing, into a previously preparedcorrection data storage portion, characteristic data obtained based on adetection result in the first characteristic detection step and adetection result in the second characteristic detection step ascorrection data for correcting a video signal; and

a video signal correction step of correcting the video signal based onthe correction data stored in the correction data storage portion, togenerate a data signal to be supplied to the n×m pixel circuits,

wherein

one frame period includes a selection period in which light emission ofthe electro-optic element is prepared and a light emission period inwhich light emission of the electro-optic element is performed,

pieces of processing of one or both of the first characteristicdetection step and the second characteristic detection step areperformed only on one row of the pixel matrix in each one frame period,and

the processing of the second characteristic detection step is performedin the light emission period.

According to a second aspect of the present invention, in the firstaspect of the present invention,

the pieces of processing of both the first characteristic detection stepand the second characteristic detection step are performed only on onerow of the pixel matrix in each one frame period,

when a row on which the pieces of processing of both the firstcharacteristic detection step and the second characteristic detectionstep are performed in each frame is defined as a monitor row and a rowother than the monitor row is defined as a non-monitor row, a length ofthe selection period of the monitor row is longer than a length of theselection period of the non-monitor row, and

the processing of the first characteristic detection step is performedin the selection period.

According to a third aspect of the present invention, in the firstaspect of the present invention,

the processing of one of the first characteristic detection step and thesecond characteristic detection step is performed on only one row of thepixel matrix in each one frame period,

when attention is focused on one row of the pixel matrix, the processingof the first characteristic detection step and the processing of thesecond characteristic detection step are alternately performed, and

the processing of the first characteristic detection step is performedin the light emission period.

According to a fourth aspect of the present invention, in the firstaspect of the present invention,

in the second characteristic detection step, a voltage of a positiveelectrode of the electro-optic element is measured in a state of aconstant current being given to the electro-optic element, to detect thecharacteristic of the electro-optic element.

According to a fifth aspect of the present invention, in the fourthaspect of the present invention,

in the second characteristic detection step, a length of the time forgiving the constant current to the electro-optic element is adjusted inaccordance with a target luminance.

According to a sixth aspect of the present invention, in the fourthaspect of the present invention,

in the second characteristic detection step, the constant currents at aplurality of levels are given to the electro-optic element within arange where an integrated value of a light emission current in one frameperiod becomes a value corresponding to a target gradation, to detect aplurality of characteristics as the characteristics of the electro-opticelement.

According to a seventh aspect of the present invention, in the firstaspect of the present invention,

in the second characteristic detection step, a current flowing in theelectro-optic element is measured in a state of a constant voltage beinggiven to the electro-optic element, to detect the characteristic of theelectro-optic element.

According to an eighth aspect of the present invention, in the seventhaspect of the present invention,

in the second characteristic detection step, a length of the time forgiving the constant voltage to the electro-optic element is adjusted inaccordance with a target luminance.

According to a ninth aspect of the present invention, in the seventhaspect of the present invention,

in the second characteristic detection step, the constant voltages at aplurality of levels are given to the electro-optic element within arange where an integrated value of a light emission current in one frameperiod becomes a value corresponding to a target gradation, to detect aplurality of characteristics as the characteristics of the electro-opticelement.

According to a tenth aspect of the present invention, in the firstaspect of the present invention,

in the first characteristic detection step, a current flowing between adrain and a source of the drive transistor is measured in a state ofsetting a gate-source voltage of the drive transistor to predeterminedmagnitude, to detect the characteristic of the drive transistor.

According to an eleventh aspect of the present invention, in the firstaspect of the present invention,

the correction data storage portion includes

-   -   an offset value storage portion configured to store an offset        value as the correction data, and    -   a gain value storage portion configured to store a gain value as        the correction data,

in the correction data storage step,

-   -   the sum of an offset value obtained based on the detection        result in the first characteristic detection step and an offset        value obtained based on the detection result in the second        characteristic detection step is stored as a new offset value        into the offset value storage portion, and    -   the product of a gain value obtained based on the detection        result in the first characteristic detection step and a        correction coefficient obtained based on the detection result in        the second characteristic detection step is stored as a new gain        value into the gain value storage portion.

According to a twelfth aspect of the present invention, in the eleventhaspect of the present invention,

the display device further includes

-   -   a characteristic detection portion configured to detect the        characteristic of the drive transistor and the characteristic of        the electro-optic element, and    -   m monitor lines which are provided so as to correspond to        respective columns of the pixel matrix and are configured so as        to be made electrically connectable with the characteristic        detection portion and the pixel circuits on the corresponding        column,

the selection period includes a first period in which the processing ofthe first characteristic detection step is performed and a second periodsubsequent to the first period, and

when a value of a difference between the offset value stored in theoffset value storage portion and the offset value obtained based on thedetection result in the first characteristic detection step is definedas a first value and a value obtained based on the gain value stored inthe gain value storage portion and the gain value obtained based on thedetection result in the first characteristic detection step is definedas a second value, a voltage corresponding to the sum of the first valueand the second value is applied to each monitor line in the secondperiod.

According to a thirteenth aspect of the present invention, in the firstaspect of the present invention,

the correction data storage portion includes

-   -   a drive transistor offset value storage portion configured to        store an offset value corresponding to the drive transistor as        the correction data,    -   an electro-optic element offset value storage portion configured        to store an offset value corresponding to the electro-optic        element as the correction data,    -   a drive transistor gain value storage portion configured to        store a gain value corresponding to the drive transistor as the        correction data, and    -   an electro-optic element gain value storage portion configured        to store a gain value corresponding to the electro-optic element        as the correction data, and

in the correction data storage step,

-   -   an offset value obtained based on the detection result in the        first characteristic detection step is stored as a new offset        value into the drive transistor offset value storage portion,    -   a gain value obtained based on the detection result in the first        characteristic detection step is stored as a new gain value into        the drive transistor gain value storage portion,    -   an offset value obtained based on the detection result in the        second characteristic detection step is stored as a new offset        value into the electro-optic element offset value storage        portion, and    -   a correction coefficient obtained based on the detection result        in the second characteristic detection step is stored as a new        gain value into the electro-optic element gain value storage        portion.

According to a fourteenth aspect of the present invention, in thethirteenth aspect of the present invention,

in the second characteristic detection step, a voltage of a positiveelectrode of the electro-optic element is measured in a state of aconstant current being given to the electro-optic element, to detect thecharacteristic of the electro-optic element, and

magnitude of the constant current is adjusted in accordance with thegain value stored in the electro-optic element gain value storageportion.

According to a fifteenth aspect of the present invention, in thethirteenth aspect of the present invention,

in the second characteristic detection step, a current flowing in theelectro-optic element is measured in a state of a constant voltage beinggiven to the electro-optic element, to detect the characteristic of theelectro-optic element, and

magnitude of the constant voltage is adjusted in accordance with thegain value stored in the electro-optic element gain value storageportion.

According to a sixteenth aspect of the present invention, in thethirteenth aspect of the present invention,

the display device further includes

-   -   a characteristic detection portion configured to detect the        characteristic of the drive transistor and the characteristic of        the electro-optic element, and    -   m monitor lines which are provided so as to correspond to        respective columns of the pixel matrix and are configured so as        to be made electrically connectable with the characteristic        detection portion and the pixel circuits on the corresponding        column,

the selection period includes a first period in which the processing ofthe first characteristic detection step is performed and a second periodsubsequent to the first period, and

in the second period, a voltage corresponding to the sum of the offsetvalue stored in the electro-optic element offset value storage portionand a value obtained based on the gain value stored in the electro-opticelement gain value storage portion is applied to each monitor line.

According to a seventeenth aspect of the present invention, in the firstaspect of the present invention,

the display device further includes

-   -   a characteristic detection portion which includes at least a        current measurement portion configured to measure a current and        detects the characteristic of the drive transistor and the        characteristic of the electro-optic element, and    -   m monitor lines which are provided so as to correspond to        respective columns of the pixel matrix and are configured so as        to be made electrically connectable with the characteristic        detection portion and the pixel circuits on the corresponding        column, and

in the first characteristic detection step, a current flowing between adrain and a source of the drive transistor is measured by the currentmeasurement portion in a state of setting a gate-source voltage of thedrive transistor to predetermined magnitude, in a state where the mmonitor lines are electrically connected to the corresponding pixelcircuits and the current measurement portion.

According to an eighteenth aspect of the present invention, in theseventeenth aspect of the present invention,

the characteristic detection portion further includes a voltagemeasurement portion configured to measure a voltage, and

in the second characteristic detection step, a voltage of a positiveelectrode of the electro-optic element is measured by the voltagemeasurement portion in a state of a constant current being given to theelectro-optic element.

According to a nineteenth aspect of the present invention, in theseventeenth aspect of the present invention,

in the second characteristic detection step, a current flowing in theelectro-optic element is measured by the current measurement portion ina state of a constant voltage being given to the electro-optic element.

According to a twentieth aspect of the present invention, in theseventeenth aspect of the present invention,

only one characteristic detection portion is provided for each K monitorlines (K is an integer not smaller than 2 and not larger than m),

and in each frame,

-   -   one of the K monitor lines is electrically connected to the        characteristic detection portion, and    -   the monitor line not electrically connected to the        characteristic detection portion is put in a high impedance        state.

According to a twenty-first aspect of the present invention, in thefirst aspect of the present invention,

the processing of the second characteristic detection step is notperformed as to a pixel at which a black display or an almost blackdisplay is performed out of the n-row×m-column pixel matrix.

According to a twenty-second aspect of the present invention, in thefirst aspect of the present invention,

the method for driving a display device further comprises a monitorregion storage step of storing information specifying a region where thepieces of processing of one or both of the first characteristicdetection step and the second characteristic detection step are lastperformed into a previously prepared monitor region storage portionduring power-off of the display device, wherein,

after power-on of the display device, the pieces of processing of one orboth of the first characteristic detection step and the secondcharacteristic detection step are performed from a region in a vicinityof a region obtained based on the information stored in the monitorregion storage portion.

According to a twenty-third aspect of the present invention, in thefirst aspect of the present invention,

the method for driving a display device further comprises:

a temperature detection step of detecting a temperature; and

a temperature change compensation step of correcting the characteristicdata based on the temperature detected in the temperature detectionstep, wherein,

in the correction data storage step, data obtained by the processing ofthe temperature change compensation step is stored as the correctiondata into the correction data storage portion.

According to a twenty-fourth aspect of the present invention, in thefirst aspect of the present invention,

the drive transistor is a thin-film transistor with a channel layerformed of an oxide semiconductor.

According to a twenty-fifth aspect of the present invention, in thetwenty-fourth aspect of the present invention,

the oxide semiconductor is indium gallium zinc oxide mainly composed ofindium (In), gallium (Ga), zinc (Zn), and oxygen (O).

A twenty-sixth aspect of the present invention is directed to a displaydevice having an n-row×m-column (a and m are integers not smaller than2) pixel matrix including n×m pixel circuits each including anelectro-optic element whose luminance is controlled by a current and adrive transistor configured to control a current to be supplied to theelectro-optic element, the display device comprising:

a pixel circuit drive portion configured to drive the n×m pixel circuitswhile performing a first characteristic detection processing fordetecting a characteristic of the drive transistor and a secondcharacteristic detection processing for detecting a characteristic ofthe electro-optic element;

a correction data storage portion configured to store characteristicdata obtained based on a detection result in the first characteristicdetection processing and a detection result in the second characteristicdetection processing as correction data for correcting a video signal;and

a video signal correction portion configured to correct the video signalbased on the correction data stored in the correction data storageportion, to generate a data signal to be supplied to the n×m pixelcircuits,

wherein

one frame period includes a selection period in which light emission ofthe electro-optic element is prepared and a light emission period inwhich light emission of the electro-optic element is performed, and

the pixel circuit drive portion performs one or both of the firstcharacteristic detection processing and the second characteristicdetection processing for only one row of the pixel matrix in each oneframe period, and performs the second characteristic detectionprocessing in the light emission period.

Effects of the Invention

According to the first aspect of the present invention, in a displaydevice including a pixel circuit that includes an electro-optic element(e.g., an organic EL element) whose luminance is controlled by a currentand a drive transistor configured to control a current to be supplied tothe electro-optic element, detection of a characteristic of the drivetransistor and detection of a characteristic of the electro-opticelement are performed. Then, a video signal is corrected by use ofcorrection data obtained in consideration of detection results of boththe drive transistor and the electro-optic element. Since a data signalbased on the video signal corrected in this manner is supplied to thepixel circuit, a drive current with such magnitude as to compensate forthe degradation of the drive transistor and the degradation of theelectro-optic element is supplied to the electro-optic element. Here,detection of the characteristic of the electro-optic element isperformed during a light emission period of the electro-optic element.This prevents the length of the light emission period from becomingshorter than the length of the conventional light emission period due tothe detection of the characteristic of the drive transistor and theelectro-optic element. Thus, it is possible to simultaneously compensatefor both degradation of the drive transistor and degradation of theelectro-optic element without causing special light emission at the timeof detecting characteristics in a display device.

According to the second aspect of the present invention, the length ofthe selection period of a monitor row (row on which the characteristicis detected in each frame) is longer than the length of the selectionperiod of a non-monitor row. Then, detection of the characteristic ofthe drive transistor is performed in that selection period. Hence aperiod for detecting the characteristic of the drive transistor issufficiently ensured.

According to the third aspect of the present invention, both detectionof the characteristic of the drive transistor and detection of thecharacteristic of the electro-optic element are performed during thelight emission period of the electro-optic element. Therefore,differently from the configuration where detection of the characteristicis also performed during the selection period, the selection period ofthe monitor row is not required to be made long. This ensures the lightemission period with a sufficient length. Further, this preventsoccurrence of variations in length of the selection period depending onthe row. As described above, in the display device, it is possible tosimultaneously compensate for both the degradation of the drivetransistor and the degradation of the electro-optic element withoutcausing special light emission at the time of detecting characteristics,while sufficiently ensuring the light emission period without occurrenceof variations in length of the selection period.

According to the fourth aspect of the present invention, a constantcurrent is supplied to the electro-optic element which is subjected todetection of the characteristic. Therefore, by adjusting the time forsupplying the constant current to the electro-optic element, it ispossible to make the electro-optic element emit light with a desiredluminance.

According to the fifth aspect of the present invention, it is possibleto make the electro-optic element emit light with a desired luminancewhile detecting the characteristic of the electro-optic element.

According to the sixth aspect of the present invention, since aplurality of characteristics are detected as the characteristics of theelectro-optic element, it is possible to more effectively compensate forthe degradation of the drive transistor.

According to the seventh aspect of the present invention, it is possibleto reduce the measurement time for detecting the characteristic of theelectro-optic element.

According to the eighth aspect of the present invention, it is possibleto make the electro-optic element emit light with a desired luminancewhile detecting the characteristic of the electro-optic element.

According to the ninth aspect of the present invention, since aplurality of characteristics are detected as the characteristics of theelectro-optic element, it is possible to more effectively compensate forthe degradation of the drive transistor.

According to the tenth aspect of the present invention, it is possibleto exert a similar effect to that of the first aspect of the presentinvention in the mode of the display device being provided withconstitutional elements for measuring a current.

According to the eleventh aspect of the present invention, correctiondata in consideration of both the characteristic of the drive transistorand the characteristic of the electro-optic element is stored into theoffset value storage portion, and correction data in consideration ofboth the characteristic of the drive transistor and the characteristicof the electro-optic element is also stored into the gain value storageportion. Hence it is possible to facilitate correction of the videosignal in consideration of both the characteristic of the drivetransistor and the characteristic of the electro-optic element.

According to the twelfth aspect of the present invention, a voltage inaccordance with the degree of degradation of the electro-optic elementis applied to a monitor line before the light emission period, to reducethe length of the charging time in the light emission period.

According to the thirteenth aspect of the present invention, the storageportion configured to store an offset value and the storage portionconfigured to store a gain value are each separated into a storageportion used for compensating for the degradation of the drivetransistor and a storage portion used for compensating for thedegradation of the electro-optic element. Hence it is possible to adjusta current that is supplied to the electro-optic element in considerationonly of the degradation of the electro-optic element. At that time, byincreasing a current according to a degradation level of a pixel withthe least degradation, it is possible to perform compensation onburning.

According to the fourteenth aspect of the present invention, concerningdetection of the characteristic of the electro-optic element, themagnitude of the current that is supplied to the electro-optic elementin the light emission period is adjusted in accordance with the gainvalue (correction coefficient) stored in the electro-optic element gainvalue storage portion. That is, the magnitude of the current is adjustedin accordance with the degree of degradation of the electro-opticelement. This leads to compensation for deterioration in currentefficiency.

According to the fifteenth aspect of the present invention, concerningdetection of the characteristic of the electro-optic element, themagnitude of the voltage that is given to the electro-optic element inthe light emission period is adjusted in accordance with the gain value(correction coefficient) stored in the electro-optic element gain valuestorage portion. Thereby, a voltage having magnitude in accordance withthe degree of degradation of the electro-optic element is given to theelectro-optic element in the light emission period.

According to the sixteenth aspect of the present invention, a voltage inaccordance with the degree of degradation of the electro-optic elementis applied to a monitor line before the light emission period, to reducethe length of the charging time in the light emission period.

According to the seventeenth aspect of the present invention,characteristics of both the drive transistor and the electro-opticelement included in each column can be detected by one monitor line.

According to the eighteenth aspect of the present invention, theelectro-optic element emits light so as to make a display with agradation close to a desired gradation.

According to the nineteenth aspect of the present invention, it ispossible to reduce the measurement time for detecting the characteristicof the electro-optic element.

According to the twentieth aspect of the present invention, onecharacteristic detection portion is shared by a plurality of monitorlines. Hence it is possible to simultaneously compensate for bothdegradation of the drive transistor and degradation of the electro-opticelement without causing special light emission at the time of detectingcharacteristics, while suppressing an increase in circuit area.

According to the twenty-first aspect of the present invention,unnecessary light emission of the electro-optic element is prevented.

According to the twenty-second aspect of the present invention, adifference in number of times of detection of the characteristic of thedrive transistor and the characteristic of the electro-optic elementbetween, for example, an upper row and a lower row is prevented frombeing generated. Hence it is possible to uniformly compensate for thedegradation of the drive transistor and the degradation of theelectro-optic element throughout the screen, so as to effectivelyprevent occurrence of variations in luminance.

According to the twenty-third aspect of the present invention, a videosignal is corrected by use of correction data in consideration of atemperature change. Therefore, in the display device, it is possible tosimultaneously compensate for both the degradation of the drivetransistor and the degradation of the electro-optic element withoutcausing special light emission at the time of detecting characteristicsregardless of a temperature change.

According to the twenty-fourth aspect of the present invention, a thinfilm transistor with a channel layer formed of an oxide semiconductor isused as the drive transistor provided in the pixel circuit. Hence it ispossible to obtain the effects of high definition and low powerconsumption. Further, since an off-current becomes extremely small, itis possible to obtain the effect of being able to ensure a sufficientS/N ratio at the time of detecting a current.

According to the twenty-fifth aspect of the present invention, by use ofindium gallium zinc oxide as the oxide semiconductor that forms thechannel layer, it is possible to reliably achieve a similar effect tothat of the twenty-fourth aspect of the present invention.

According to the twenty-sixth aspect of the present invention, it ispossible to exert a similar effect to that of the first aspect of thepresent invention in the invention of a display device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart for explaining an outline of an operation relatedto detection of a TFT characteristic and an OLED characteristic in afirst embodiment of the present invention.

FIG. 2 is a block diagram showing a whole configuration of an organic ELdisplay device in the first embodiment.

FIG. 3 is a timing chart for explaining an operation of a gate driver inthe first embodiment.

FIG. 4 is a timing chart for explaining the operation of the gate driverin the first embodiment.

FIG. 5 is a timing chart for explaining the operation of the gate driverin the first embodiment.

FIG. 6 is a block diagram showing a schematic configuration of a signalconversion circuit in the first embodiment.

FIG. 7 is a diagram showing a configuration of a pixel circuit and amonitor circuit in the first embodiment.

FIG. 8 is a diagram showing one constitutional example of a currentmeasurement portion in the first embodiment.

FIG. 9 is a diagram showing one constitutional example of a voltagemeasurement portion in the first embodiment.

FIG. 10 is a diagram for explaining shifting of an operation on each rowin the first embodiment.

FIG. 11 is a diagram for explaining a flow of a current at the time of anormal operation being performed in the first embodiment.

FIG. 12 is a timing chart for explaining an operation of a pixel circuit(a pixel circuit on the ith row and the jth column) included in amonitor row in the first embodiment.

FIG. 13 is a diagram for explaining a flow of a current in a TFTcharacteristic detection period in the first embodiment.

FIG. 14 is a diagram for explaining application of a reference voltageto a data line in the TFT characteristic detection period in the firstembodiment.

FIG. 15 is a diagram for explaining a flow of a current in a lightemission period in the first embodiment.

FIG. 16 is a diagram for explaining adjustment of light emission time ofthe organic EL element in the first embodiment.

FIG. 17 is a diagram for explaining a difference in length of the lightemission period between a monitor row and a non-monitor row in the firstembodiment.

FIG. 18 is a flowchart for explaining a procedure for updating an offsetmemory and a gain memory in the first embodiment.

FIG. 19 is a diagram showing a configuration of a video signalcorrection portion in the first embodiment.

FIG. 20 is a diagram for explaining an effect in the first embodiment.

FIG. 21 is a block diagram showing a whole configuration of an organicEL display device in a first modified example of the first embodiment.

FIG. 22 is a flowchart for explaining a procedure for updating a TFToffset memory, an OLED offset memory, a TFT gain memory, and an OLEDgain memory in the first modified example of the first embodiment.

FIG. 23 is a diagram for explaining an effect in the first modifiedexample of the first embodiment.

FIG. 24 is a diagram showing a configuration in the vicinity of one endof a monitor line in a second modified example of the first embodiment.

FIG. 25 is a diagram showing a configuration in the vicinity of one endof a monitor line in a third modified example of the first embodiment.

FIG. 26 is a block diagram showing a whole configuration of an organicEL display device of a fourth modified example of the first embodiment.

FIG. 27 is a diagram for explaining temperature dependency of acurrent-voltage characteristic of an organic EL element.

FIG. 28 is a block diagram showing a whole configuration of an organicEL display device in a fifth modified example of the first embodiment.

FIG. 29 is a flowchart for explaining a procedure for updating an offsetmemory and a gain memory in the fifth modified example of the firstembodiment.

FIG. 30 is a diagram showing a detailed configuration of a monitorcircuit in a sixth modified example of the first embodiment.

FIG. 31 is a block diagram showing a whole configuration of an activematrix-type organic EL display device according to a second embodimentof the present invention.

FIG. 32 is a timing chart for explaining an operation of a gate driverin the second embodiment.

FIG. 33 is a timing chart for explaining the operation of the cratedriver in the second embodiment.

FIG. 34 is a timing chart for explaining the operation of the gatedriver in the second embodiment.

FIG. 35 is a diagram showing a configuration of a pixel circuit and amonitor circuit in the second embodiment.

FIG. 36 is a diagram for explaining shifting of an operation on each rowin the second embodiment.

FIG. 37 is a diagram for explaining a flow of a current at the time of anormal operation being performed in the second embodiment.

FIG. 38 is a timing chart for explaining an OLED characteristicdetecting operation in a pixel circuit (a pixel circuit on the ith rowand the jth column) included in a monitor row in the second embodiment.

FIG. 39 is a diagram for explaining a flow of a current at the time ofthe OLED characteristic detecting operation being performed in thesecond embodiment.

FIG. 40 is a timing chart for explaining a TFT characteristic detectingoperation in a pixel circuit (a pixel circuit on the ith row and the jthcolumn) included in the monitor row in the second embodiment.

FIG. 41 is a diagram for explaining a flow of a current at the time ofthe TFT characteristic detecting operation being performed in the secondembodiment.

FIG. 42 is a flowchart for explaining a procedure for updating an offsetmemory and a gain memory in the second embodiment.

FIG. 43 is a diagram for explaining shifting of an operation on each rowin a modified example of the second embodiment.

FIG. 44 is a circuit diagram showing a configuration of a conventionalgeneral pixel circuit.

FIG. 45 is a timing chart for explaining an operation of the pixelcircuit shown in FIG. 44.

FIG. 46 is a diagram for explaining a case where no compensation isperformed on degradation of the drive transistor and degradation of theorganic EL element.

FIG. 47 is a diagram for explaining a case where compensation isperformed only on the degradation of the drive transistor.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference to the attached drawings. In addition, it is assumed in thefollowing that m and n are integers not smaller than 2, i is an integernot smaller than 1 and not larger than n, and j is an integer notsmaller than 1 and not larger than m. Further, in the following, acharacteristic of a drive transistor provided in a pixel circuit isreferred to as a “TFT characteristic”, and a characteristic of anorganic EL element provided in the pixel circuit is referred to as an“OLED characteristic”.

1. First Embodiment 1.1 Whole Configuration

FIG. 2 is a block diagram showing a whole configuration of an activematrix-type organic EL display device 1 according to a first embodimentof the present invention. This organic EL display device 1 is providedwith a display portion 10, a control circuit 20, a source driver (a dataline drive circuit) 30, a gate driver (a scanning line drive circuit)40, an offset memory 51, and a gain memory 52. It is to be noted thatone or both of the source driver 30 and the gate driver 40 may beconfigured to be integrally formed with the display portion 10. Further,the offset memory 51 and the gain memory 52 may be physically formed ofone memory.

It should be noted that the pixel circuit drive portion is realized bythe source driver 30 and the gate driver 40, and the correction datastorage portion is realized by the offset memory 51 and the gain memory52, in the present embodiment.

The display portion 10 is provided with m data lines S(1) to S(m) and nscanning lines G1(1) to G1(n) orthogonal thereto. Hereinafter, anextending direction of the data line is referred to as a Y-direction,and an extending direction of the scanning line is referred to as anX-direction. A constitutional element along the Y-direction may bereferred to as a “column”, and a constitutional element along theX-direction may be referred to as a “row”. Further, the display portion10 is provided with m monitor lines M(1) to M(m) so as to correspond tothe m data lines S(1) to S(m) one-to-one. The data lines S(1) to S(m)and the monitor lines M(1) to M(m) are parallel to each other. Moreover,the display portion 10 is provided with n monitor control lines G2(1) toG2(n) so as to correspond to the n scanning lines G1(1) to G1(n)one-to-one. The scanning lines G1(1) to G1(n) and the monitor controllines G2(1) to G2(n) are parallel to each other. Furthermore, thedisplay portion 10 is provided with n×m pixel circuits 11 so as tocorrespond to intersections of the n scanning lines G1(1) to G1(n) andthe m data lines S(1) to S(m). By the n×m pixel circuits 11 beingprovided in this manner, an n-row×m-column pixel matrix is formed on thedisplay portion 10. Further, the display portion 10 is provided with ahigh-level power supply line for supplying a high-level power supplyvoltage, and a low-level power supply line for supplying a low-levelpower supply voltage.

It is to be noted that in the following, the data line is simply denotedby symbol S when the m data lines S(1) to S(m) are not required to bedistinguished from each other. Similarly, the monitor line is simplydenoted by symbol M when the m monitor lines M(1) to M(m) are notrequired to be distinguished from each other. The scanning line issimply denoted by symbol G1 when the n scanning lines G1(1) to G1(n) arenot required to be distinguished from each other. The monitor controlline is simply denoted by symbol G2 when the n monitor control linesG2(1) to G2(n) are not required to be distinguished from each other.

The control circuit 20 controls an operation of the source driver 30 bygiving a data signal DA, a source control signal SCTL, and a switchingcontrol signal SW to the source driver 30, and controls an operation ofthe gate driver 40 by transmitting a gate control signal GCTL to thegate driver 40. The source control signal SCTL includes a source startpulse, a source clock, and a latch strobe signal, for example. The gatecontrol signal GCTL includes a gate start pulse and a gate clock, forexample. Further, the control circuit 20 receives monitor data MO givenfrom the source driver 30, and updates the offset memory 51 and the gainmemory 52. It should be noted that the monitor data MO is data measuredfor obtaining the TFT characteristic and the OLED characteristic.

The gate driver 40 is connected to the n scanning lines G1(1) to G1(n)and the n monitor control lines G2(1) to G2(n). The gate driver 40 isformed of a shift register, a logic circuit, and the like. Incidentally,in the organic EL display device 1 according to the present embodiment,a video signal transmitted from the outside (data to be an original ofthe data signal DA) is corrected based on the TFT characteristic and theOLED characteristic. Concerning this, detection of the TFTcharacteristic and the OLED characteristic for one row is performed ineach frame. That is, when detection of the TFT characteristic and theOLED characteristic for the first row is performed in one frame,detection of the TFT characteristic and the OLED characteristic for thesecond row is performed in the next frame, and further, detection of theTFT characteristic and the OLED characteristic for the third row isperformed in the further next frame. In this manner, detection of theTFT characteristic and the OLED characteristic for n rows is performedby taking n frame periods. Here, when the frame in which detection ofthe TFT characteristic and the OLED characteristic for the first row isperformed is defined as a (k+1) th frame, the n scanning lines G1(1) toG1(n) and the n monitor control lines G2(1) to G2(n) are driven as shownin FIG. 3 in the (k+1)th frame. They are driven as shown in FIG. 4 inthe (k+2)th frame, and driven as shown in FIG. 5 in the (k+n)th frame.It should be noted that, concerning FIGS. 3 to 5, a high-level state isan active state. Further, a period in which the scanning line G1 is inthe active state is referred to as a “selection period”. This selectionperiod is a period for preparing light emission of the organic ELelement provided in the pixel circuit 11. As grasped from FIGS. 3 to 5,only a scanning line corresponding to a row on which detection of theTFT characteristic and the OLED characteristic is performed is put inthe active state for a longer period than the other scanning lines, ineach frame. Hereinafter, the row on which detection of the TFTcharacteristic and the OLED characteristic is performed when attentionis focused on any frame is referred to as a “monitor row”, and a rowother than the monitor row is referred to as a “non-monitor row”. Ineach frame, the monitor control line G2 corresponding to the non-monitorrow is held in a non-active state. The monitor control line G2corresponding to the monitor row is put in the active state in a firstpredetermined period out of the selection period, and is put in thenon-active state in the remaining period in the selection period.Thereafter, the monitor control line G2 is again put in the active statein a period till the time almost one frame period after the start pointof the selection period. In the present embodiment, the gate driver 40is configured such that the n scanning lines G1(1) to G1(n) and the nmonitor control lines G2(1) to G2(n) are driven as described above.

The source driver 30 is connected to the m data lines S(1) to S(m) andthe m monitor lines M(1) to M(m). The source driver 30 is formed of adrive signal generation circuit 31, a signal conversion circuit 32, andan output portion 33 including m output circuits 330. Each of the moutput circuits 330 in the output portion 33 is connected to thecorresponding data line S out of the m data lines S(1) to S(m) and thecorresponding monitor line M out of the m monitor lines M(1) to M(m).

The drive signal generation circuit 31 includes a shift register, asampling circuit, and a latch circuit. In the drive signal generationcircuit 31, the shift register sequentially transmits the source startpulse from the input end to the output end in synchronization with thesource clock. In accordance with this transmission of the source startpulse, a sampling pulse corresponding to each data line S is outputtedfrom the shift register. The sampling circuit sequentially stores thedata signal DA for one row in accordance with the timing of the samplingpulse. The latch circuit fetches and holds the data signal DA for onerow stored in the sampling circuit in accordance with the latch strobesignal.

FIG. 6 is a block diagram showing a schematic configuration of thesignal conversion circuit 32. As shown in FIG. 6, the signal conversioncircuit 32 is formed of a gradation signal generation circuit 321 and amonitor circuit 322. The gradation signal generation circuit 321includes a D/A converter. The data signal DA for one row held in thelatch circuit in the drive signal generation circuit 31 as describedabove is converted to an analog voltage by the D/A converter in thegradation signal generation circuit 321. The converted analog voltage isgiven to the output circuit 330 in the output portion 33. The monitorcircuit 322 includes an A/D converter. In the A/D converter in themonitor circuit 322, an analog voltage, which appears on the monitorline M and represents the TFT characteristic and the OLEDcharacteristic, is converted to the monitor data MO as a digital signal.The monitor data MO is given to the control circuit 20 via the drivesignal generation circuit 31. It is to be noted that the monitor circuit322 will be described in detail later.

The output circuit 330 in the output portion 33 applies the analogvoltage, which is given from the gradation signal generation circuit 321in the signal conversion circuit 32, as a data voltage to the data lineS via a buffer. Further, the output circuit 330 in the output portion 33switches connection destination of the monitor line M based on theswitching control signal SW. It should be noted that this will bedescribed in detail later.

The offset memory 51 and the gain memory 52 store correction data usedfor correcting the video signal transmitted from the outside. Morespecifically, the offset memory 51 stores an offset value as correctiondata, and the gain memory 52 stores a gain value as correction data. Itshould be noted that typically, the same number of offset values andgain values as the number of pixels in the display portion 10 arerespectively stored into the offset memory 51 and the gain memory 52.Further, a buffer memory for temporarily holding an offset value(hereinafter referred to as an “offset value buffer”) and a buffermemory for temporarily holding a gain value (hereinafter referred to asa “gain value buffer”) are provided in the control circuit 20, forexample. Based on the monitor data MO given from the source driver 30,the control circuit 20 updates the offset value in the offset memory 51and the gain value in the gain memory 52. Further, the control circuit20 reads the offset value stored in the offset memory 51 and the gainvalue stored in the gain memory 52, and corrects the video signal. Dataobtained by the correction is transmitted as the data signal DA to thesource driver 30.

1.2 Configuration of Pixel Circuit and Monitor Circuit

FIG. 7 is a diagram showing configurations of the pixel circuit 11 andthe monitor circuit 322. It is to be noted that the pixel circuit 11shown in FIG. 7 is the pixel circuit 11 on the ith row and the jthcolumn. This pixel circuit 11 is provided with one organic EL elementOLED, three transistors T1 to T3, and one capacitor Cst. The transistorT1 functions as an input transistor for selecting a pixel, thetransistor T2 functions as a drive transistor for controlling supply ofa current to the organic EL element OLED, and the transistor T3functions as a monitor control transistor for controlling whether or notto detect the TFT characteristic and the OLED characteristic.

The transistor T1 is provided between the data line S(j) and a gateterminal of the transistor T2. As for the transistor T1, a gate terminalis connected to the scanning line G1(i), and a source terminal isconnected to the data line S(j). The transistor T2 is provided in serieswith the organic EL element OLED. As for the transistor T2, a gateterminal is connected to the drain terminal of the transistor T1, adrain terminal is connected to a high-level power supply line ELVDD, anda source terminal is connected to an anode terminal of the organic ELelement OLED. As for the transistor T3, a gate terminal is connected tothe monitor control line G2(i), a drain terminal is connected to theanode terminal of the organic EL element OLED, and a source terminal isconnected to the monitor line M(j). As for the capacitor Cst, one end isconnected to the gate terminal of the transistor T2, and the other endis connected to the source terminal of the transistor T2. A cathodeterminal of the organic EL element OLED is connected to the low-levelpower supply line ELVSS.

In the present embodiment, the transistors T1 to T3 in the pixel circuit11 are all n-channel transistors. Further, in the present embodiment, anoxide TFT (thin film transistor using an oxide semiconductor for achannel layer) is employed for each of the transistors T1 to T3.Specifically, there is employed an IGZO-TFT where a channel layer isformed of InGaZnOx (indium gallium zinc oxide) (hereinafter referred toas “IGZO”; “IGZO” is a registered trademark) which is an oxidesemiconductor mainly composed of indium (In), gallium (Ga), zinc (Zn)and oxygen (O). It is to be noted that the oxide TFT such as theIGZO-TFT is effective especially in the case of being employed as then-channel transistor included in the pixel circuit 11. However, thepresent invention does not exclude the use of a p-channel type oxideTFT. Further, it is also possible to employ a transistor using an oxidesemiconductor other than IGZO for the channel layer. For example, asimilar effect is obtained in the case of employing a transistor usingan oxide semiconductor containing at least one of indium, gallium, zinc,copper (Cu), silicon (Si), tin (Sn), aluminum (Al), calcium (Ca),germanium (Ge), and lead (Pb) for the channel layer. Moreover, thepresent invention does not exclude the use of a transistor other thanthe transistor using the oxide semiconductor for the channel layer.

As shown in FIG. 7, the monitor circuit 322 includes a currentmeasurement portion 38 and a voltage measurement portion 39. In thepresent embodiment, the characteristic detection portion is realized bythis monitor circuit 322. Concerning the relationship among the currentmeasurement portion 38, the voltage measurement portion 39, and themonitor line M(j), the monitor line M(j) is configured to connect toeither the current measurement portion 38 or the voltage measurementportion 39 based on the switching control signal SW given from thecontrol circuit 20 to the output circuit 330. It is to be noted thatFIG. 7 shows only part of a configuration of the output circuit 330.

FIG. 8 is a diagram showing one constitutional example of the currentmeasurement portion 38. This current measurement portion 38 includes anoperation amplifier 381, a capacitor 382, a switch 383, and an A/Dconverter 384. As for the operation amplifier 381, a non-inverting inputterminal is connected to the low-level power supply line ELVSS, and aninverting input terminal is connected to the monitor line M. Thecapacitor 382 and the switch 383 are provided between an output terminalof the operation amplifier 381 and the monitor line M. As describedabove, this current measurement portion 38 is formed of an integrationcircuit. In such a configuration, first, the switch 383 is brought intoan on-state by a control clock signal Sclk. This brings the statebetween the output terminal and the inverting input terminal of theoperation amplifier 381 into a short-circuited state, and potentials ofthe output terminal of the operation amplifier 381 and the monitor lineM become equal to a potential of the low-level power supply line ELVSS.At the time of detecting a current, the switch 383 is brought into anoff-state by the control clock signal Sclk. Thereby, due to theexistence of the capacitor 382, the potential of the output terminal ofthe operation amplifier 381 changes in accordance with magnitude of acurrent flowing in the monitor line M. That change in potential isreflected to a digital signal outputted from the A/D converter 384. Thedigital signal is then outputted as the monitor data MO from the currentmeasurement portion 38.

FIG. 9 is a diagram showing one constitutional example of the voltagemeasurement portion 39. This voltage measurement portion 39 includes anamplifier 391 and an A/D converter 392. In such a configuration, with aconstant current being allowed to flow in the monitor line M by aconstant current source 37, a voltage between a node 393 and thelow-level power supply line ELVSS is amplified by the amplifier 391.Then, a voltage after the amplification is converted to a digital signalby the A/D converter 392. The digital signal is then outputted as themonitor data MO from the voltage measurement portion 39.

1.3 Drive Method

Next, a driving method in the present embodiment will be described. Asdescribed above, in the present embodiment, detection of the TFTcharacteristic and the OLED characteristic for one row is performed ineach frame. In each frame, an operation for detecting the TFTcharacteristic and the OLED characteristic (hereinafter referred to as a“characteristic detecting operation”) is performed on the monitor row,and a normal operation is performed on the non-monitor row. That is,when a frame in which detection of the TFT characteristic and the OLEDcharacteristic for the first row is performed is defined as a (k+1)thframe, an operation on each row is shifted as shown in FIG. 10. Further,when detection of the TFT characteristic and the OLED characteristic isperformed, the offset memory 51 and the gain memory 52 are updated byuse of detection results thereof. The video signal is then corrected byuse of the correction data stored in the offset memory 51 and the gainmemory 52.

<1.3.1 Operation of Pixel Circuit>

<1.3.1.1 Normal Operation>

In each frame, the normal operation is performed on the non-monitor row.In the pixel circuit 11 included in the non-monitor row, after writingbased on a data voltage corresponding to a target luminance is performedin the selection period, the transistor T1 is held in the off-state. Thetransistor T2 comes into the on-state by the writing based on the datavoltage. The transistor T3 is held in the off-state. Thus, a drivecurrent is supplied to the organic EL element OLED via the transistor T2as indicated by an arrow denoted by reference numeral 71 in FIG. 11.Thereby, the organic EL element OLED emits light with a luminance inaccordance with the drive current.

<1.3.1.2 Characteristic Detecting Operation>

In each frame, the characteristic detecting operation is performed onthe monitor row. FIG. 12 is a timing chart for explaining an operationof the pixel circuit 11 (assumed to be the pixel circuit 11 on the ithrow and the jth column) included in the monitor row. It should be notedthat FIG. 12 shows “one frame period”, taking as a reference the startpoint of the selection period of the ith row in the frame in which theith row is the monitor row. As for the monitor row, as shown in FIG. 12,one frame period includes: a period Ta for detecting the TFTcharacteristic (hereinafter such a period will be referred to as a “TFTcharacteristic detection period”); a period Tb for writing datacorresponding to a black display (hereinafter such a period will bereferred to as a “black writing period”); and a period Tc for making theorganic EL element OLED emit light (hereinafter such a period will bereferred to as a “light emission period”). A first predetermined periodout of the selection period is the TFT characteristic detection periodTa, and a period other than the TFT characteristic detection period Taout of the selection period is the black writing period Tb. It is to benoted that the first period is realized by the TFT characteristicdetection period Ta and the second period is realized by the blackwriting period Tb in the present embodiment.

In the TFT characteristic detection period Ta, the scanning line G1(i)and the monitor control line G2(i) are put in the active state. Thisbrings the transistor T1 and the transistor T3 into the on-state.Further, in the TFT characteristic detection period T1, a referencevoltage Vref for detecting the TFT characteristic is applied to the dataline S(j). Thereby, the reference voltage Vref is written and thetransistor T2 also comes into the on-state. As a result, a currentflowing in the transistor T2 is outputted to the monitor line M(j) viathe transistor T3 as indicated by an arrow denoted by reference numeral72 in FIG. 13. Further, in the TFT characteristic detection period Ta,the monitor line M(j) is connected to the current measurement portion 38by the switching control signal SW. Thereby, the current (sink current)outputted to the monitor line M(j) is measured by the currentmeasurement portion 38. In such a manner as above, the magnitude of thecurrent flowing between the drain and the source of the transistor T2 ismeasured in the state of setting a gate-source voltage of the transistorT2 to predetermined magnitude (magnitude of the reference voltage Vref),and the TFT characteristic is detected.

Incidentally, in the present embodiment, as shown in FIG. 14, two kindsof reference voltages (first reference voltage Vref1 and secondreference voltage Vref2) are applied as the reference voltage Vref tothe data line S(j) in the TFT characteristic detection period Ta.Accordingly a TFT characteristic based on the first reference voltageVref1 and a TFT characteristic based on the second reference voltageVref2 are detected.

In the black writing period Tb, the scanning line G1(i) is held in theactive state, and the monitor control line G2(i) is put in thenon-active state. Thereby, the transistor T1 is held in the on-state andthe transistor T3 comes into the off-state. Further, in the blackwriting period Tb, a voltage Vblack corresponding to a black display isapplied to the data line S(j), and hence the transistor T2 comes intothe off-state. Thus, a current does not flow in the transistor T2. It isto be noted that the monitor line M(j) is applied with a voltage beingthe sum of “a difference between the offset value stored in the offsetmemory 51 and the offset value obtained in the TFT characteristicdetection period Ta” (first value) and “a voltage corresponding to alight emission voltage calculated from the gain value stored in the gainmemory 52 and the gain value obtained in the TFT characteristicdetection period Ta” (second value) in the black writing period Tb.Thereby, a voltage in accordance with the degree of degradation of theorganic EL element OLED is applied to the monitor line M(j) before thelight emission period Tc, and the length of the charging time in thelight emission period Tc is reduced.

In the light emission period Tc, the scanning line G1(i) is put in thenon-active state, and the monitor control line G2(i) is put in theactive state. Here, since writing based on the voltage Vblackcorresponding to a black display is performed in the black writingperiod Tb before the light emission period Tc, the transistor T2 is inthe off-state. Further, in the period for detecting the OLEDcharacteristic out of the light emission period Tc, the monitor lineM(j) is connected to the voltage measurement portion 39, and theconstant current is supplied to the monitor line M(j). Thereby, a datacurrent as the constant current is supplied from the monitor line M(j)to the organic EL element OLED as indicated by an arrow denoted byreference numeral 73 in FIG. 15. In this state, a light emission voltageof the organic EL element OLED is measured by the voltage measurementportion 39. As described above, the OLED characteristic is detected bymeasuring the voltage of the positive electrode of the organic ELelement OLED in the state where the constant current is being given tothe organic EL element OLED.

Incidentally, the data current that is supplied to the organic ELelement OLED in the light emission period Tc is the constant current.For this reason, in the present embodiment, the length of the time forlight emitting of the organic EL element OLED is adjusted in order tomake a display with a desired gradation. For example, the constantcurrent is set to be a current corresponding to a white display, and thehigher the gradation is, the longer the light emission time is made,while the lower the gradation is, the shorter the light emission time ismade. To realize this, for example, the higher the gradation is, thelonger the period Tc1 in which the monitor line M is connected to thevoltage measurement portion 39 is made, and the lower the gradation is,the longer the period Tc2 in which the monitor line M is connected tothe current measurement portion 38 is made, as shown in FIG. 16. At thattime, the lengths of the periods Tc1 and Tc2 are adjusted based on adegradation correction coefficient obtained from a difference betweenthe gain value stored in the gain memory 52 and the gain value obtainedin the TFT characteristic detection period Ta. As described above, thelength of the time for light emitting of the organic EL element OLED isadjusted such that an integrated value of the light emission current inone frame period becomes a value corresponding to a desired gradation.In other words, the length of the time for giving the constant currentto the organic EL element OLED is adjusted in accordance with a targetluminance. It should be noted that, when the integrated value of thelight emission current in one frame period becomes a value correspondingto a desired gradation, the current value may be changed during thelight emission period Tc, to measure the characteristic (current-voltagecharacteristic) at a plurality of operation points. Further, theconfiguration may be such that the length of the time for light emittingof the organic EL element OLED is made uniform and the current value ischanged in accordance with a gradation. In this case, the magnitude ofthe current that is supplied to the monitor line M may be obtained basedon a degradation correction coefficient obtained from a differencebetween the gain value stored in the gain memory 52 and the gain valueobtained in the TFT characteristic detection period Ta. It should benoted that, since the gain value in consideration of both the TFTcharacteristic and the OLED characteristic has been stored in the gainmemory 52, the difference between the gain value stored in the gainmemory 52 and the gain value obtained in the TFT characteristicdetection period Ta becomes a value representing the OLEDcharacteristic.

Further, in the present embodiment, the length of the selection periodof the monitor row is longer than that of the non-monitor row as shownin FIG. 17. Hence there is a difference in length of the light emissionperiod between the monitor row and the non-monitor row. Then, the datacurrent is adjusted such that the integrated value of the light emissioncurrent in one frame period becomes a value corresponding to a desiredgradation.

It should be noted that, when a gradation as a target is a gradationcorresponding to a black display or a gradation close thereto, it ispreferable not to detect the OLED characteristic. That is, it ispreferable not to detect the OLED characteristic at a pixel where ablack display or an almost black display is made out of then-row×m-column pixel matrix. This enables prevention of unnecessarylight emission. The organic EL element OLED is not degraded when it doesnot emit light, and hence there is no need for detecting itscharacteristic.

<1.3.2 Updating of Offset Memory and Gain Memory>

Next, a description will be given to how the offset value stored in theoffset memory 51 and the gain value stored in the gain memory 52 areupdated. FIG. 18 is a flowchart for explaining a procedure for updatingthe offset memory 51 and the gain memory 52. It is to be noted thathere, attention is focused on an offset value and a gain value eachcorresponding to one pixel.

First, in the first half of the TFT characteristic detection period Ta,the TFT characteristic based on the first reference voltage Vref1 isdetected (step S110). By this step S110, an offset value for correctingthe video signal is obtained. The offset value obtained in step S110 isstored into the offset value buffer (step S120). In the last half of theTFT characteristic detection period Ta, the TFT characteristic based onthe second reference voltage Vref2 is detected (step S130). By this stepS130, a gain value for correcting the video signal is obtained. The gainvalue obtained in step S130 is stored into the gain value buffer (stepS140).

Thereafter, in the light emission period Tc, the OLED characteristic isdetected (step S150). By this step S150, a degradation correctioncoefficient and an offset value for correcting the video signal areobtained. Then, the sum of the offset value stored in the offset valuebuffer and the offset value obtained in step S150 is stored as a newoffset value into the offset memory 51 (step S160). Further, the productof the gain value stored in the gain value buffer and the degradationcorrection coefficient obtained in step S150 is stored as a new gainvalue into the gain memory 52 (step S170).

In such a manner as above, the offset value and the gain value eachcorresponding to one pixel are updated. In the present embodiment, sincedetection of the TFT characteristic and the OLED characteristic for onerow is performed in each frame, m offset values in the offset memory 51and m gain values in the gain memory 52 are updated in each one frame.

It is to be noted that the characteristic data is realized by data(offset value, gain value, degradation correction coefficient) obtainedbased on detection results in steps S110, S130 and S150 in the presentembodiment.

Incidentally, as described above, the light emission voltage of theorganic EL element OLED is measured in the light emission period Tc. Thelarger the detected voltage as a measurement result thereof is, thelarger the degree of degradation of the organic EL element OLED is.Therefore, the offset memory 51 and the gain memory 52 are updated suchthat the larger the detected voltage is the larger the offset value andthe gain value become.

<1.3.3 Correction of Video Signal>

In the present embodiment, in order to compensate for the degradation ofthe drive transistor and the degradation of the organic EL element OLED,the video signal transmitted from the outside is corrected by use of thecorrection data stored in the offset memory 51 and the gain memory 52.Hereinafter, this correction of the video signal will be described.

Correction of the video signal transmitted from the outside is performedin a video signal correction portion (not shown) in the control circuit20. FIG. 19 is a diagram showing a configuration of the video signalcorrection portion. The video signal correction portion is provided withan LUT 211, a multiplication portion 212, and an addition portion 213.In such a configuration, a value of the video signal corresponding toeach pixel is corrected as follows.

First, the video signal transmitted from the outside is subjected togamma correction by use of the LUT 211. That is, a gradation P indicatedby the video signal is converted to a control voltage Vc by the gammacorrection. The multiplication portion 212 receives the control voltageVc and a gain value B read from the gain memory 52, and outputs a value“Vc·B” obtained by multiplying the control voltage Vc and the gain valueB. The addition portion 213 receives the value “Vc·B” outputted from themultiplication portion 212 and an offset value Vt read from the offsetmemory 51, and outputs a value “Vc·B+Vt” obtained by adding the value“Vc·B” and the offset value Vt. The value “Vc·B+Vt” obtained asdescribed above is transmitted as the data signal DA from the controlcircuit 20 to the source driver 30.

<1.3.4 Summary of Driving Method>

FIG. 1 is a flowchart for explaining an outline of an operation relatedto detection of the TFT characteristic and the OLED characteristic.First, on the monitor row, detection of the TFT characteristic isperformed in the TFT characteristic detection period Ta (step S10).Next, on the monitor row, detection of the OLED characteristic isperformed in the light emission period Tc (step S20). Thereafter,updating of the offset memory 51 and the gain memory 52 is performed byuse of detection results in the steps S10 and S20. Then, correction ofthe video signal transmitted from the outside is performed by use of thecorrection data stored in the offset memory 51 and the gain memory 52(step S40).

It is to be noted that the first characteristic detection step isrealized by step S10, the second characteristic detection step isrealized by step S20, the correction data storage step is realized bystep S30, and the video signal correction step is realized by step S40,in the present embodiment. Further, the first characteristic detectionprocessing is realized by the processing of step S10, and the secondcharacteristic detection processing is realized by the processing ofstep S20.

1.4 Effects

According to the present embodiment, detection of the TFT characteristicand the OLED characteristic for one row is performed in each frame. Whenattention is focused on the monitor row, in one frame period, the TFTcharacteristic is detected in a certain period (TFT characteristicdetection period Ta) during the selection period, and the OLEDcharacteristic is detected during the light emission period. Then, thevideo signal transmitted from the outside is corrected by use ofcorrection data (offset value and gain value) obtained in considerationof both a detection result of the TFT characteristic and a detectionresult of the OLED characteristic. Since a data voltage based on thevideo signal (the data signal DA) corrected in this manner is applied tothe data line S, a drive current with such magnitude as to compensatefor the degradation of the drive transistor and the degradation of theorganic EL element OLED is supplied to the organic EL element OLED, atthe time of making the organic EL element OLED in each pixel circuit 11emit light (see FIG. 20). Here, detection of the OLED characteristic isperformed during the light emission period as described above. Thisprevents the length of the light emission period from becoming shorterthan that of the conventional light emission period due to detection ofthe TFT characteristic and the OLED characteristic. As described above,according to the present embodiment, it is possible to simultaneouslycompensate for both the degradation of the drive transistor and thedegradation of the organic EL element OLED without causing special lightemission at the time of detecting characteristics in the organic ELdisplay device.

Further, in the present embodiment, since an oxide TFT (specifically,IGZO-TFT) is employed for each of the transistors T1 to T3 in the pixelcircuit 11, it is possible to obtain the effect of being able to ensurea sufficient S/N ratio. This will be described below. When the IGZO-TFTis compared with an LTPS (Low Temperature Poly Silicon) —TFT,off-current is extremely smaller in the IGZO-TFT than in the LTPS-TFT.For example, when the LTPS-TFT is employed for the transistor T3 in thepixel circuit 11, the off-current becomes approximately 1 pA at themaximum. In contrast, when the IGZO-TFT is employed for the transistorT3 in the pixel circuit 11, the off-current becomes approximately 10 fAat the maximum. Hence, for example, the off-current for 1000 rowsbecomes approximately 1 nA at the maximum when the LTPS-TFT is employed,and it becomes approximately 10 pA at the maximum when the IGZO-TFT isemployed. A detected current is approximately from 10 to 100 nA wheneither TFT is employed. Incidentally, the monitor line M is connected tothe pixel circuit 11 on the non-monitor row as well as to the pixelcircuit 11 on the monitor row. Therefore, the S/N ratio of the monitorline M depends on the sum of leak currents of the transistors T3 on thenon-monitor rows. Specifically, the S/N ratio of the monitor line M isrepresented by “detected current/(leak current×number of non-monitorrows)”. Thus, for example in the organic EL display device having thedisplay portion 10 of “Landscape FHD”, the S/N ratio becomesapproximately 10 when the LTPS-TFT is employed, whereas the S/N ratiobecomes approximately 1000 when the IGZO-TFT is employed. In thismanner, in the present embodiment, it is possible to ensure a sufficientS/N ratio at the time of detecting a current.

1.5 Modified Example>

Hereinafter, modified examples of the first embodiment will bedescribed. It should be noted that in the following, only aspectsdifferent from the first embodiment will be described in detail, anddescriptions of similar aspects to the first embodiment will be omitted.

1.5.1 First Modified Example>

FIG. 21 is a block diagram showing a whole configuration of an activematrix-type organic EL display device 2 according to a first modifiedexample of the first embodiment. In the present modified example, inplace of the offset memory 51 and the gain memory 52 in the firstembodiment, a TFT offset memory 51 a, an OLED offset memory 51 b, a TFTgain memory 52 a, and an OLED gain memory 52 b are provided. That is, inthe present modified example, each of the offset memory and the gainmemory is divided into a memory used for compensating for thedegradation of the drive transistor and a memory used for compensatingfor the degradation of the organic EL element OLED.

The TFT offset memory 51 a stores an offset value based on the detectionresult of the TFT characteristic. The OLED offset memory 51 b stores anoffset value based on the detection result of the OLED characteristic.The TFT gain memory 52 a stores a gain value based on the detectionresult of the TFT characteristic. The OLED gain memory 52 b stores adegradation correction coefficient based on the detection result of theOLED characteristic.

Concerning the characteristic detecting operation (FIG. 12), in thepresent modified example, the monitor line M is applied with a voltagebeing the sum of “the offset value stored in the OLED offset memory 51b” and “a voltage corresponding to a light emission voltage calculatedfrom the degradation correction coefficient stored in the OLED gainmemory 52 b” in the black writing period Tb. Further, the length of thelight emission time of the organic EL element OLED is adjusted based onthe degradation correction coefficient stored in the OLED gain memory 52b. In the case of employing the configuration where the length of thelight emission time of the organic EL element OLED is made constant anda current value is changed in accordance with a gradation, the magnitudeof the current that is supplied to the monitor line M may be obtainedbased on the degradation correction coefficient stored in the OLED gainmemory 52 b.

Next, updating of the offset memory and the gain memory in the presentmodified example will be described. FIG. 22 is a flowchart forexplaining a procedure for updating the TFT offset memory 51 a, the OLEDoffset memory 51 b, the TFT gain memory 52 a, and the OLED gain memory52 b. It is to be noted that here, attention is focused on an offsetvalue and a gain value each corresponding to one pixel.

First, in the first half of the TFT characteristic detection period Ta,the TFT characteristic is detected based on the first reference voltageVref1 (step S210). By this step S210, an offset value for correcting thevideo signal is obtained. Then, the offset value obtained in step S210is stored as a new offset value into the TFT offset memory 51 a (stepS220). In the last half of the TFT characteristic detection period Ta,the TFT characteristic is detected based on the second reference voltageVref2 (step S230). By this step S230, a gain value for correcting thevideo signal is obtained. Then, the gain value obtained in step S230 isstored as a new gain value into the TFT gain memory 52 a (step S240).Thereafter, in the light emission period Tc, the OLED characteristic isdetected (step S250). By this step S250, a degradation correctioncoefficient and an offset value for correcting the video signal areobtained. Then, the offset value obtained in step S250 is stored as anew offset value into the OLED offset memory 51 b (step S260). Further,the degradation correction coefficient obtained in step S250 is storedas a new degradation correction coefficient into the OLED gain memory 52b (step S270). In the present modified example, as described above, theoffset memory and the gain memory are updated.

Next, the effect of the present modified example will be described.Concerning the characteristic detecting operation (FIG. 12), assumingthat the potential of the monitor line M is made equal to the potentialof the low-level power supply line ELVSS in the black writing period Tb,a delay may occur depending on a capacity of the monitor line M at thetime of writing in the light emission period Tc. Time t_charge requiredfor charging is represented by the following formula (1) when adifference between the light emission voltage of the organic EL elementand the potential of the monitor line M immediately before writing isVd; the magnitude of the current that is written into the monitor line Mis i_L; and a load of the monitor line M is Cmp.

t_charge=Cmp·Vd/i _(—) L  (1)

Here, when Vd is 3V, i_L is 10 nA, and Cmp is 30 pF, the time t_chargerequired for charging is 9 milliseconds. When a drive frequency is 60Hz, the length of one frame period is about 16 milliseconds, and hence aperiod not shorter than a half of one frame period is spent forcharging. In this respect, in the present modified example, the monitorline M is applied with the voltage being the sum of “the offset valuestored in the OLED offset memory 51 b” and “the voltage corresponding tothe light emission voltage calculated from the degradation correctioncoefficient stored in the OLED gain memory 52 b” in the black writingperiod Tb. That is, before the light emission period Tc, the monitorline M is previously charged such that the potential of the monitor lineM becomes a potential close to a light emission threshold of the organicEL element OLED. Thereby, Vd in the formula (1) decreases, leading toreduction in time required for charging.

Further, according to the present modified example, at the time of thecharacteristic detecting operation on the monitor row, the current thatis supplied from the monitor line M to the organic EL element OLED inthe light emission period To is adjusted based on the degradationcorrection coefficient stored in the OLED gain memory 52 b. That is, thecurrent is adjusted in accordance with the degree of degradation of theorganic EL element OLED, thereby leading to compensation fordeterioration in current efficiency. It should be noted that, at thetime of the normal operation on the non-monitor row, compensation inconsideration of both the degradation of the drive transistor and thedegradation of the organic EL element OLED is performed.

Moreover, in the present modified example, each of the offset memory andthe gain memory is divided into the memory used for compensating for thedegradation of the drive transistor and the memory used for compensatingfor the degradation of the organic EL element OLED. Hence it is possibleto adjust the current that is supplied to the organic EL element inconsideration only of the degradation of the organic EL element OLED. Atthat time, by increasing the current according to a degradation level ofa pixel with the least degradation as shown in FIG. 23, it is possibleto perform compensation on burning.

1.5.2 Second Modified Example

In the first embodiment, the monitor line M is configured to connect toeither the current measurement portion 38 or the voltage measurementportion 39 as shown in FIG. 7. However, the present invention is notrestricted to this, and it is also possible to employ a configurationwhere the monitor line M can be brought into the high impedance state(configuration of the present modified example).

FIG. 24 is a diagram showing a configuration in the vicinity of one endof the monitor line M in the present modified example. As grasped fromFIG. 24, the monitor line M is brought into any of the state of beingconnected to the current measurement portion 38, the state of beingconnected to the voltage measurement portion 39 and the high impedancestate by the switching control signal SW, in the present modifiedexample.

Incidentally, in the first embodiment, concerning adjustment of thelength of the light emission time of the organic EL element OLED in thelight emission period Tc (see FIG. 12), the higher the gradation is, thelonger the period Tc1 in which the monitor line M is connected to thevoltage measurement portion 39 is made, and the lower the gradation is,the longer the period Tc2 in which the monitor line M is connected tothe current measurement portion 38 is made, as shown in FIG. 16. Incontrast, according to the present modified example, the monitor line Mcan be brought into the high impedance state instead of being connectedto the current measurement portion 38.

1.5.3 Third Modified Example

In the first embodiment, the description has been given on the premisethat one monitor circuit 322 including the current measurement portion38 and the voltage measurement portion 39 is provided for one column.However, the present invention is not restricted to this, and it is alsopossible to employ a configuration where one monitor circuit 322 isshared by a plurality of columns (configuration of the present modifiedexample).

In the present modified example, similarly to the second modifiedexample (see FIG. 24), the monitor line M is brought into any of thestate of being connected to the current measurement portion 38, thestate of being connected to the voltage measurement portion 39, and thehigh impedance state. Further, in the present modified example, thevicinity of one end of the monitor line M has a configuration shown inFIG. 25. That is, one monitor circuit 322 is provided for each K monitorlines M.

In such a configuration as above, in each frame, only one column out ofK columns corresponding to the K monitor lines M is taken as a column onwhich detection of the TFT characteristic and the OLED characteristic isperformed (hereinafter referred to as a “characteristic detection objectcolumn). At the time of the characteristic detecting operation on themonitor row, the monitor lines M on the columns other than thecharacteristic detection object column are held in the high impedancestate. Further, at the time of the characteristic detecting operation onthe monitor row, not the reference voltage Vref but a normal datavoltage (voltage corresponding to a target luminance) is applied to adata line D on the columns other than the characteristic detectionobject column. During the light emission period Tc, the transistor T3 isin the on-state on the monitor row, but the monitor line M is in thehigh impedance state on the columns other than the characteristicdetection object column. For this reason, on each of the columns otherthan the characteristic detection object column, a current does not flowin the monitor line M but flows in the organic EL element OLED, and theorganic EL element OLED emits light as in the normal operation. On thecharacteristic detection object column out of the monitor row, theforegoing characteristic detecting operation is performed.

For example, in the organic EL display device having the display portion10 of “Landscape FHD” and a drive frequency of 60 Hz, the time requiredfor monitoring (detection of the TFT characteristic and the OLEDcharacteristic) for one column is 18 seconds (=1080/60). Here, in orderto make an offset value and a gain value each corresponding to eachpixel updated, for example, every 30 minutes (1800 seconds), theconfiguration may be such that one monitor circuit 322 is provided foreach 100 monitor lines M.

Thus, according to the present modified example, it is possible tosimultaneously compensate for both the degradation of the drivetransistor and the degradation of the organic EL element OLED withoutcausing special light emission at the time of detecting characteristics,while suppressing an increase in circuit area, in the organic EL displaydevice.

1.5.4 Fourth Modified Example

According to the first embodiment, when a short-time operation of theorganic EL display device 1 is repeated, there is generated a largedifference in number of times of detection of the TFT characteristic andthe OLED characteristic between an upper row of the display portion 10and a lower row of the display portion 10. Then, in an organic ELdisplay device 3 according to the present modified example, a monitorrow storage portion 201 for storing a monitor row is provided in thecontrol circuit 20 as shown in FIG. 26. In such a configuration, at thetime of power-off, information specifying a row on which the TFTcharacteristic and the OLED characteristic have been last detected isstored into the monitor row storage portion 201. The monitor regionstorage step is realized by this processing. After power-on, the TFTcharacteristic and the OLED characteristic are detected from a row nextto the row specified based on the information stored in the monitor rowstorage portion 201. It should be noted that the monitor region storageportion is realized by the monitor row storage portion 201 in thepresent embodiment.

Thus, according to the present modified example, a difference in numberof times of detection of the TFT characteristic and the OLEDcharacteristic between the upper row of the display portion 10 and thelower row of the display portion 10 is prevented from being generated.Hence it is possible to uniformly compensate for the degradation of thedrive transistor and the degradation of the organic EL element OLEDthroughout the screen, so as to effectively prevent occurrence ofvariations in luminance.

It is to be noted that the row on which the TFT characteristic and theOLED characteristic are first detected after the power-on is notrestricted to the row next to the row specified based on the informationstored in the monitor row storage portion 201. It may be a row in thevicinity of the row specified based on the information stored in themonitor row storage portion 201. For example, there may exist a row onwhich the characteristic detecting operation is performed twiceimmediately before the power-off and immediately after the power-on.

Further, information specifying a column on which the TFT characteristicand the OLED characteristic have been last detected may be stored, orinformation specifying both the row and the column on which the TFTcharacteristic and the OLED characteristic have been last detected maybe stored.

1.5.5 Fifth Modified Example

FIG. 27 is a diagram for explaining temperature dependency of acurrent-voltage characteristic of the organic EL element. FIG. 27 showsa current-voltage characteristic of the organic EL element at atemperature TE1, a current-voltage characteristic of the organic ELelement at a temperature TE2, and a current-voltage characteristic ofthe organic EL element at a temperature TE3. It is to be noted:“TE1>TE2>TE3” is satisfied. As grasped from FIG. 27, in order to supplya predetermined current to the organic EL element, the lower thetemperature is, the higher the voltage is required to be made. As thusdescribed, the current-voltage characteristic of the organic EL elementdepends greatly on the temperature. Hence it is preferable to employ aconfiguration capable of compensating for a temperature change(configuration of the present modified example).

FIG. 28 is a block diagram showing a whole configuration of an organicEL display device 4 in the present modified example. In the presentmodified example, a temperature sensor 60 is provided in addition to theconstitutional elements in the first embodiment. Further, the controlcircuit 20 is provided with a temperature change compensation portion202. The temperature sensor 60 gives temperature information TE as aresult of measurement of a temperature to the control circuit 20 asneeded. The temperature change compensation portion 202 makes correctionon the monitor data MO given from the source driver 30 based on thetemperature information TE. Specifically, the temperature changecompensation portion 202 converts a value of the monitor data MOcorresponding to a temperature at the time of detection to a valuecorresponding to a certain standard temperature, and updates the offsetvalue in the offset memory 51 and the gain value in the gain memory 52based on the value obtained by the conversion.

It is to be noted that the temperature detection step is realized by theprocessing of the temperature sensor 60, and the temperature changecompensation step is realized by the processing of the temperaturechange compensation portion 202.

FIG. 29 is a flowchart for explaining a procedure for updating theoffset memory 51 and the gain memory 52 in the present modified example.It is to be noted that the pieces of processing in steps S310 to S350 inthe present modified example (FIG. 29) are the same as those in stepsS110 to S150 in the first embodiment (FIG. 18), and the pieces ofprocessing in steps S360 to S370 in the present modified example (FIG.29) are the same as those in steps S160 and S170 in the first embodiment(FIG. 18). In the present modified example, the offset value and thegain value are corrected based on the temperature information TE givenby the temperature sensor 60 after the OLED characteristic has beendetected and before the offset value and the gain value are updated(step S355).

Thus, according to the present modified example, the video signaltransmitted from the outside is corrected by correction data (offsetvalue and gain value) in consideration of the temperature change.Therefore, it is possible to simultaneously compensate for both thedegradation of the drive transistor and the degradation of the organicEL element OLED regardless of the temperature change, in the organic ELdisplay device.

1.5.6 Sixth Modified Example

In the first embodiment, detection of the OLED characteristic isperformed by measuring the voltage of the positive electrode of theorganic EL element OLED in the state where the constant current is givento the organic EL element OLED. However, the present invention is notrestricted to this. The configuration may be such that detection of theOLED characteristic is performed by measuring a current flowing in theorganic EL element OLED in the state of a constant voltage being givento the organic EL element OLED (configuration of the present modifiedexample).

In the present modified example, both detection of the TFTcharacteristic and detection of the OLED characteristic are performed bymeasuring a current. Therefore, there is no need to provide aconstitutional element for measuring a voltage in the monitor circuit.Accordingly, in the present modified example, the configuration of themonitor circuit is different from that in the first embodiment. FIG. 30is a diagram showing a detailed configuration of a monitor circuit 323in the present modified example. This monitor circuit 323 includes anoperation amplifier 3231, a capacitor 3232, a first switch 3233, asecond switch 3234, an offset and amplifier ratio adjustment portion3235, and an A/D converter 3236. As for the operation amplifier 3231, anon-inverting input terminal is connected to the second switch 3234, andan inverting input terminal is connected to the monitor line M. Thecapacitor 3232 and the first switch 3233 are provided between an outputterminal of the operation amplifier 3231 and the monitor line M. Theoffset and amplifier ratio adjustment portion 3235 is provided betweenthe output terminal of the operation amplifier 3231 and the A/Dconverter 3236. The second switch 3234 functions as a switch forswitching a potential of the non-inverting input terminal of theoperation amplifier 3231 between the potential of the low-level powersupply line ELVSS and an OLED characteristic detection potential Vel. Asthus described, this monitor circuit 323 is formed of an integrationcircuit. It is to be noted that the OLED characteristic detectionpotential Vel is a potential corresponding to the sum of “a differencebetween the offset value stored in the offset memory 51 and the offsetvalue obtained in the TFT characteristic detection period Ta” (firstvalue) and “a voltage corresponding to a light emission voltagecalculated from the gain value stored in the gain memory 52 and the gainvalue obtained in the TFT characteristic detection period Ta” (secondvalue).

In such a configuration as above, at the time of measuring a current fordetecting the TFT characteristic, a similar operation to that in thefirst embodiment is performed in a state where the potential of thenon-inverting input terminal of the operation amplifier 3231 is set tothe potential of the low-level power supply line ELVSS by a secondcontrol clock signal Sclk2. At the time of measuring a current fordetecting the OLED characteristic, first, the first switch 3233 isbrought into the on-state by a first control clock signal Sclk1, whilethe potential of the non-inverting input terminal of the operationamplifier 3231 is set to the OLED characteristic detection potential Velby the second control clock signal Sclk2. This brings the state betweenthe output terminal and the inverting input terminal of the operationamplifier 3231 into the short-circuited state, and the potential of themonitor line M becomes equal to the OLED characteristic detectionpotential Vel. Then, the first switch 3233 is brought into the off-stateby the first control clock signal Sclk1. Accordingly, due to theexistence of the capacitor 3232, the potential of the output terminal ofthe operation amplifier 3231 changes in accordance with magnitude of acurrent flowing in the monitor line M(a source current that is suppliedto the organic EL element OLED). That change in potential is reflectedto a digital signal that is outputted from the A/D converter 3236. Thedigital signal is then outputted as the monitor data MO from the monitorcircuit 323. It is to be noted that the offset and amplifier ratioadjustment portion 3235 has the function of making the level of inputinto the A/D converter 3236 the same between the time of detecting theTFT characteristic and the time of detecting the OLED characteristic.

In the present modified example, in such a manner as above, detection ofthe OLED characteristic is performed by measuring a current flowing inthe organic EL element OLED in the state of a constant voltage beinggiven to the organic EL element OLED. This allows reduction inmeasurement time.

It is to be noted that the magnitude of the constant voltage that isgiven to the organic EL element OLED may be obtained based on adegradation correction coefficient obtained from a difference betweenthe gain value stored in the gain memory 52 and the gain value obtainedin the TFT characteristic detection period Ta. Further, in a case wherethe TFT offset memory 51 a, the OLED offset memory 51 b, the TFT gainmemory 52 a, and the OLED gain memory 52 b are provided in place of theoffset memory 51 and the gain memory 52 (see the first modifiedexample), the magnitude of the constant voltage that is given to theorganic EL element OLED may be obtained based on the degradationcorrection coefficient stored in the OLED gain memory 52 b.

Further, at the time of detecting the OLED characteristic, the length ofthe time for giving the constant voltage to the organic EL element OLEDis preferably adjusted in accordance with a target luminance. Further,when the integrated value of the light emission current in one frameperiod becomes the value corresponding to a desired gradation, a voltagevalue may be changed during the light emission period Tc, to measure thecharacteristic (current-voltage characteristic) at a plurality ofoperation points.

2.1 Second Embodiment> 2.1 Whole Configuration>

FIG. 31 is a block diagram showing a whole configuration of an activematrix-type organic EL display device 5 according to a second embodimentof the present invention. In the present embodiment, a display portion10 a is provided with n high-level power supply control lines G3(1) toG3(n) in addition to the m data lines S(1) to S(m), the m monitor linesM(1) to M(m), the n scanning lines G1(1) to G1(n), and the n monitorcontrol lines G2(1) to G2(n), as shown in FIG. 31. The scanning linesG1(1) to G1(n), the monitor control lines G2(1) to G2(n), and thehigh-level power supply control lines G3(1) to G3(n) are parallel toeach other. It is to be noted that, in the following, the high-levelpower supply control line is simply denoted by symbol G3 when the nhigh-level power supply control lines G3(1) to G3(n) are not required tobe distinguished from each other. The control circuit 20 and the sourcedriver 30 are similar to those in the first embodiment, and hencedescriptions thereof will be omitted.

Agate driver 40 a in the present embodiment is connected to the nscanning lines G1(1) to G1(n), the n monitor control lines G2(1) toG2(n), and the n high-level power supply control lines G3(1) to G3(n).The gate driver 40 a is formed of a shift register, a logic circuit, andthe like. Incidentally, in the present embodiment, differently from thefirst embodiment, either detection of the TFT characteristic for one rowor detection of the OLED characteristic for one row is performed in eachframe. It is to be noted that, concerning the present embodiment, a rowon which the TFT characteristic is detected or the OLED characteristicis detected is referred to as a “monitor row”. Further, in thefollowing, a frame in which detection of the TFT characteristic isperformed is referred to as a “TFT characteristic detection frame”, anda frame in which detection of the OLED characteristic is performed isreferred to as an “OLED characteristic detection frame”.

In the present embodiment, when detection of the OLED characteristic forthe first row is performed in one frame, detection of the OLEDcharacteristic for the second row is performed in the next frame, andfurther, detection of the OLED characteristic for the third row isperformed in the further next frame. Thereafter, the OLEDcharacteristics for the fourth to nth rows are sequentially detected.After detection of the OLED characteristic for the nth row has beenperformed, detection of the TFT characteristic for the first row isperformed. Thereafter, the TFT characteristics for the second to nthrows are sequentially detected. In this manner, detection of the TFTcharacteristic and detection of the OLED characteristic are performed indifferent frames. However, in the TFT characteristic detection frame andthe OLED characteristic detection frame, the gate driver 40 a drives thescanning line G1, the monitor control line G2, and the high-level powersupply control line G3 in the same manner.

Here, when the frame in which detection of the OLED characteristic forthe first row is performed is defined as a (k+1) th frame, the nscanning lines G1(1) to G1(n), the n monitor control lines G2(1) toG2(n), and the n high-level power supply control lines G3(1) to G3(n)are driven as shown in FIG. 32 in the (k+1) th frame. They are driven asshown in FIG. 33 in the (k+2) th frame, and they are driven as shown inFIG. 34 in the (k+n)th frame. This also applies to the frames in whichthe TFT characteristic is detected. As grasped from FIGS. 32 to 34, thelength of the selection period (period in which the scanning line G1 isin the active state) is made the same on every row, in each frame. Thatis, in the present embodiment, the length of the selection period isconstant regardless of whether or not the row is the monitor row.Further, the monitor control line G2 corresponding to the non-monitorrow is held in the non-active state, in each frame. The monitor controlline G2 corresponding to the monitor row is put in the active state fromthe start point of the selection period until the point after the lapseof the one frame period. Moreover, the high-level power supply controlline G3 corresponding to the non-monitor row is held in the activestate, in each frame. The high-level power supply control line G3corresponding to the monitor row is put in the non-active state from thestart point of the selection period until the point after the lapse ofthe one frame period. In the present embodiment, the gate driver 40 a isconfigured such that the n scanning lines G1(1) to G1(n), the n monitorcontrol lines G2(1) to G2(n), and the n high-level power supply controllines G3(1) to G3(n) are driven as described above.

Moreover, in the present embodiment, similarly to the first modifiedexample of the first embodiment, each of the offset memory and the gainmemory is divided into the memory used for compensating for thedegradation of the drive transistor and the memory used for compensatingfor the degradation of the organic EL element OLED. That is, thisorganic EL display device 5 is provided with the TFT offset memory 51 a,the OLED offset memory 51 b, the TFT gain memory 52 a and the OLED gainmemory 52 b as the constitutional elements for storing correction datato be used for correcting the video signal transmitted from the outside.

2.2 Configuration of Pixel Circuit and Monitor Circuit>

FIG. 35 is a diagram showing configurations of a pixel circuit 11 a andthe monitor circuit 322 in the present embodiment. It is to be notedthat the pixel circuit 11 a shown in FIG. 35 is the pixel circuit 11 onthe ith row and the jth column. The configuration of the monitor circuit322 is similar to that in the first embodiment, and hence descriptionsthereof will be omitted. However, in the present embodiment, theconfiguration is such that the high-level power supply voltage ELVDD issupplied to the monitor line M when the monitor line M is connected tothe current measurement portion 38.

This pixel circuit 11 a is provided with one organic EL element OLED,four transistors T1 to T4, and one capacitor Cst. The transistor T1functions as an input transistor for selecting a pixel, the transistorT2 functions as a drive transistor for controlling supply of a currentto the organic EL element OLED, the transistor T3 functions as a monitorcontrol transistor for controlling whether or not to detect the TFTcharacteristic and the OLED characteristic, and the transistor T4functions as a high-level power supply control transistor forcontrolling supply of the drive current from the high-level power supplyline ELVDD.

The transistor T1 is provided between the data line S(j) and a gateterminal of the transistor T2. As for the transistor T1, a gate terminalis connected to the scanning line G1(i), and a source terminal isconnected to the data line S). The transistor T2 is provided in serieswith the organic EL element OLED. As for the transistor T2, a gateterminal is connected to the drain terminal of the transistor T1, adrain terminal is connected to a source terminal of the transistor T4,and a source terminal is connected to an anode terminal of the organicEL element OLED. As for the transistor T3, a gate terminal is connectedto the monitor control line G2(i), a drain terminal is connected to thedrain terminal of the transistor T2, and a source terminal is connectedto the monitor line M(j). The transistor T4 is provided in series withthe organic EL element OLED. As for the transistor T4, a gate terminalis connected to the high-level power supply control line G3(i), a drainterminal is connected to the high-level power supply line ELVDD, and asource terminal is connected to the drain terminal of the transistor T2.As for the capacitor Cst, one end is connected to the gate terminal ofthe transistor T2, and the other end is connected to the source terminalof the transistor T2. A cathode terminal of the organic EL element OLEDis connected to the low-level power supply line ELVSS. For example, anoxide TFT (thin film transistor using an oxide semiconductor for achannel layer) such as the IGZO-TFT is employed for each of thetransistors T1 to T4. However, the present invention does not excludethe use of a transistor other than the oxide TFT.

2.3 Drive Method>

Next, a driving method in the present embodiment will be described. Asdescribed above, in the present embodiment, either detection of the TFTcharacteristic for one row or detection of the OLED characteristic forone row is performed in each frame. In each frame, either an operationfor detecting the TFT characteristic (hereinafter referred to as a “TFTcharacteristic detecting operation”) or an operation for detecting theOLED characteristic (hereinafter referred to as an “OLED characteristicdetecting operation”) is performed on the monitor row, and a normaloperation is performed on the non-monitor row. That is, when a frame inwhich detection of the OLED characteristic for the first row isperformed is defined as a (k+1)th frame, an operation on each row isshifted as shown in FIG. 36. It is to be noted that the TFTcharacteristic detecting operation is not performed on any row from the(k+1)th frame to the (k+n)th frame. Further, the OLED characteristicdetecting operation is not performed on any row from the (k+n+1)th frameto the (k+2n)th frame.

<2.3.1 Operation of Pixel Circuit>

<2.3.1.1 Normal Operation>

In each frame, the normal operation is performed on the non-monitor row.In the pixel circuit 11 a included in the non-monitor row, after writingbased on a data voltage corresponding to a target luminance is performedin the selection period, the transistor T1 is held in the off-state. Thetransistor T2 comes into the on-state by the writing based on the datavoltage. The transistor T3 is held in the off-state, and the transistorT4 is held in the on-state. Thus, a drive current is supplied to theorganic EL element OLED via the transistor T4 and the transistor T2 asindicated by an arrow denoted by reference numeral 74 in FIG. 37.Thereby, the organic EL element OLED emits light with a luminance inaccordance with the drive current.

<2.3.1.2 OLED Characteristic Detecting Operation>

Next, the OLED characteristic detecting operation will be described.FIG. 38 is a timing chart for explaining the OLED characteristicdetecting operation in the pixel circuit 11 a (assumed to be the pixelcircuit 11 a on the ith row and the jth column) included in the monitorrow. It should be noted that FIG. 38 shows “one frame period”, taking asa reference the start point of the selection period of the ith row inthe frame in which the ith row is the monitor row. As shown in FIG. 38,one frame period includes a selection period Tp and a light emissionperiod Tq.

In the selection period Tp, the scanning line G1(i) and the monitorcontrol line G2(i) are put in the active state. This brings thetransistor T1 and the transistor T3 into the on-state. Further, in theselection period Tp, the high-level power supply control line G3(i) isput in the non-active state. This brings the transistor T4 into theoff-state. Further, a high voltage Vlen for making the transistor T2perform a linear operation is applied to the data line S(j) in theselection period Tp. Thereby, writing based on the high voltage Vlen isperformed, and the transistor T2 comes into the on-state.

At the light emission period Tq, the scanning line G1(i) is brought intothe non-active state. This brings the transistor T1 into the off-state.Further, in the light emission period Tq, the monitor control line G2(i)is held in the active state, and the high-level power supply controlline G3(i) is held in the non-active state. Accordingly, the transistorT3 is held in the on-state and the transistor T4 is held in theoff-state. Further, since the writing based on the high voltage Vlen hasbeen performed in the selection period Tp before the light emissionperiod Tq, the transistor T2 is in the on-state. Moreover, in the periodfor detecting the OLED characteristic out of the light emission periodTq, the monitor line M(j) is connected to the voltage measurementportion 39, and the constant current is supplied to the monitor lineM(j). Thereby, a data current as the constant current is supplied fromthe monitor line M(1) to the organic EL element OLED as indicated by anarrow denoted by reference numeral 75 in FIG. 39. In this state, a lightemission voltage of the organic EL element OLED is measured by thevoltage measurement portion 39. In such a manner as above, detection ofthe OLED characteristic is performed. It should be noted that, in orderto make a display with a desired gradation, the processing of adjustingthe length of the light emission time of the organic EL element OLED andthe processing of changing a current value in accordance with agradation are performed similarly to the first embodiment.

<2.3.1.3 TFT Characteristic Detecting Operation>

Next, the TFT characteristic detecting operation will be described. FIG.40 is a timing chart for explaining the TFT characteristic detectingoperation in the pixel circuit 11 a (assumed to be the pixel circuit 11a on the ith row and the jth column) included in the monitor row.

In the selection period Tp, the scanning line G1(i) and the monitorcontrol line G2(i) are put in the active state. This brings thetransistor T1 and the transistor T3 into the on-state. Further, in theselection period Tp, the high-level power supply control line G3(i) isput in the non-active state. This brings the transistor T4 into theoff-state. Moreover, in the selection period Tp, a similar data voltageto that at the time of the normal operation is applied to the data lineS(j). The transistor T2 comes into the on-state by the writing based onthe data voltage.

At the light emission period Tq, the scanning line G1(i) is brought intothe non-active state. This brings the transistor T1 into the off-state.Further, in the light emission period Tq, the monitor control line G2(i)is held in the active state, and the high-level power supply controlline G3(i) is held in the non-active state. Accordingly, the transistorT3 is held in the on-state and the transistor T4 is held in theoff-state. Further, since the writing based on the data voltage has beenperformed in the selection period Tp before the light emission periodTq, the transistor T2 is in the on-state. Moreover, in the lightemission period Tq, the monitor line M(j) is connected to the currentmeasurement portion 38 by the switching control signal SW. Since apotential of the monitor line M(j) is equal to a potential of thehigh-level power supply line ELVDD at this time, a drive current inaccordance with the data voltage is supplied from the monitor line M(j)to the organic EL element OLED as indicated by an arrow denoted byreference numeral 76 in FIG. 41. At that time, the current supplied fromthe monitor line M(j) to the organic EL element OLED is measured by thecurrent measurement portion 38. In such a manner as above, detection ofthe TFT characteristic is performed.

<2.3.2 Updating of Offset Memory and Gain Memory

Next, updating of the offset memory and the gain memory in the presentembodiment will be described. FIG. 42 is a flowchart for explaining aprocedure for updating the TFT offset memory 51 a, the OLED offsetmemory 51 b, the TFT gain memory 52 a and the OLED gain memory 52 b. Itis to be noted that here, attention is focused on an offset value and again value each corresponding to one pixel. Incidentally, as graspedfrom FIG. 36, when attention is focused on any one pixel, detection ofthe TFT characteristic is performed after n frames from the frame inwhich detection of the OLED characteristic has been performed, in thepresent embodiment. Then, it is assumed here that detection of the OLEDcharacteristic is performed on the Kth frame and detection of the TFTcharacteristic is performed in the (K+n) th frame.

First, in the Kth frame, the OLED characteristic is detected in thelight emission period Tq (step S410). By this step S410, a degradationcorrection coefficient and an offset value for correcting the videosignal are obtained. Then, the offset value obtained in step S410 isstored as a new offset value into the OLED offset memory 51 b (stepS420). Further, the degradation correction coefficient obtained in stepS410 is stored as a new degradation correction coefficient into the OLEDgain memory 52 b (step S430). Thereafter, in the (K+n) th frame, the TFTcharacteristic is detected in the light emission period Tq (step S440).By this step S440, a gain value and an offset value for correcting thevideo signal are obtained. Then, the offset value obtained in step S440is stored as a new offset value into the TFT offset memory 51 a (stepS450). Further, the gain value obtained in step S440 is stored as a newgain value into the TFT gain memory 52 a (step S460).

In such a manner as above, the offset value and the gain value eachcorresponding to one pixel are updated. In the present embodiment,either detection of the OLED characteristic for one row or detection ofthe TFT characteristic for one row is performed in each frame.Therefore, m offset values in the OLED offset memory 51 b and mdegradation correction coefficients in the OLED gain memory 52 b areupdated in each one frame at the frames in which detection of the OLEDcharacteristic is performed, and m offset values in the TFT offsetmemory 51 a and m gain values in the TFT gain memory 52 a are updated ineach one frame at the frames in which detection of the TFTcharacteristic is performed.

<2.3.3 Correction of Video Signal>

As for correction of the video signal transmitted from the outside, thegain value B that is given to the multiplication portion 212 shown inFIG. 19 and the offset value Vt that is given to the addition portion213 shown in FIG. 19 are different from those in the first embodiment.In the present embodiment, the product of a value read from the TFT gainmemory 52 a and a value read from the OLED gain memory 52 b is given asthe gain value B to the multiplication portion 212, and the sum of avalue read from the TFT offset memory 51 a and a value read from theOLED offset memory 51 b is given as the offset value Vt to the additionportion 213. On such a premise, the gradation P indicated by the videosignal is corrected to “Vc·B+Vt”. It is to be noted that Vc is a valueof the control voltage after gamma correction on the gradation P.

2.4 Effect

According to the present embodiment, at each pixel, detection of theOLED characteristic and detection of the TFT characteristic arealternately performed with respect to each n frames (n is the number ofrows constituting the pixel matrix). Then, similarly to the firstembodiment, the video signal transmitted from the outside is correctedby use of correction data (offset value and gain value) obtained inconsideration of both a detection result of the OLED characteristic anda detection result of the TFT characteristic. Therefore, at the time ofmaking the organic EL element OLED in each pixel circuit 11 a emitlight, a drive current with such magnitude as to compensate for both thedegradation of the drive transistor and the degradation of the organicEL element OLED is supplied to the organic EL element OLED. Here, in thepresent embodiment, both detection of the OLED characteristic anddetection of the TFT characteristic are performed during the lightemission period. Therefore, differently from the configuration wheredetection of the characteristics is performed during the selectionperiod, the selection period of the monitor row is not required to bemade long. This ensures the light emission period with a sufficientlength. Further, variations in length of the selection period dependingon the row are prevented from occurring. As described above, accordingto the present embodiment, it is possible to simultaneously compensatefor both the degradation of the drive transistor and the degradation ofthe organic EL element OLED without causing special light emission atthe time of detecting characteristics, while sufficiently ensuring thelight emission period without occurrence of variations in length of theselection period, in the organic EL display device.

2.5 Modified Example>

In the second embodiment, first, detection of the OLED characteristicsfor the first to nth rows is performed sequentially one frame by oneframe, and thereafter, detection of the TFT characteristics for thefirst to nth rows is performed sequentially one frame by one frame, asshown in FIG. 36. However, the present invention is not restricted tothis. The configuration may be such that detection of the OLEDcharacteristic for the first row and detection of the TFT characteristicfor the first row each is performed one frame by one frame in twoconsecutive frames, and a similar operation is repeated for the secondto nth rows, as shown in FIG. 43.

According to the present modified example, detection of the OLEDcharacteristic and detection of the TFT characteristic are performed foreach pixel in two consecutive frame periods, and hence it is possible toemploy a configuration where the offset memory and the gain memory areupdated by use of the buffers (offset value buffer and gain valuebuffer) as in the first embodiment. That is, although the TFT offsetmemory 51 a, the OLED offset memory 51 b, the TFT gain memory 52 a, andthe OLED gain memory 52 b are provided for storing correction data to beused for correcting the video signal in the second embodiment, oneoffset memory and one gain memory may be provided in place of thosememories in the present modified example.

3. Others

The organic EL display device, to which the present invention isapplicable, is not restricted to one provided with the pixel circuit 11or 11 a illustrated in each of the embodiments and each of the modifiedexamples. The pixel circuit may have a configuration other than theconfiguration illustrated in each of the embodiments and each of themodified examples, so long as being provided with the electro-opticelement (organic EL element OLED) that is controlled by a current, thetransistors T1 to T3, and the capacitor Cst.

DESCRIPTION OF REFERENCE CHARACTERS

-   -   1 to 5: ORGANIC EL DISPLAY DEVICE    -   10, 10 a: DISPLAY PORTION    -   11, 11 a: PIXEL CIRCUIT    -   20: CONTROL CIRCUIT    -   30: SOURCE DRIVER    -   31: DRIVE SIGNAL GENERATION CIRCUIT    -   32: SIGNAL CONVERSION CIRCUIT    -   33: OUTPUT PORTION    -   38: CURRENT MEASUREMENT PORTION    -   39: VOLTAGE MEASUREMENT PORTION    -   40, 40 a: GATE DRIVER    -   51: OFFSET MEMORY    -   51 a: TFT OFFSET MEMORY    -   51 b: OLED OFFSET MEMORY    -   52: GAIN MEMORY    -   52 a: TFT GAIN MEMORY    -   52 b: OLED GAIN MEMORY    -   60: TEMPERATURE SENSOR    -   201: MONITOR ROW STORAGE PORTION    -   202: TEMPERATURE CHANGE COMPENSATION PORTION    -   321: GRADATION SIGNAL GENERATION CIRCUIT    -   322, 323: MONITOR CIRCUIT    -   330: OUTPUT CIRCUIT    -   T1 to T4: TRANSISTOR    -   Cst: CAPACITOR    -   G1(1) to G1(n): SCANNING LINE    -   G2(1) to G2(n): MONITOR CONTROL LINE    -   G3(1) to G3(n): HIGH-LEVEL POWER SUPPLY CONTROL LINE    -   S(1) to S(m): DATA LINE    -   M(1) to M(m): MONITOR LINE

1. A method for driving a display device having an n-row×m-column (n andm are integers not smaller than 2) pixel matrix including n×m pixelcircuits each including an electro-optic element whose luminance iscontrolled by a current and a drive transistor configured to control acurrent to be supplied to the electro-optic element, the methodcomprising: a first characteristic detection step of detecting acharacteristic of the drive transistor; a second characteristicdetection step of detecting a characteristic of the electro-opticelement; a correction data storage step of storing, into a previouslyprepared correction data storage portion, characteristic data obtainedbased on a detection result in the first characteristic detection stepand a detection result in the second characteristic detection step ascorrection data for correcting a video signal; and a video signalcorrection step of correcting the video signal based on the correctiondata stored in the correction data storage portion, to generate a datasignal to be supplied to the n×m pixel circuits, wherein one frameperiod includes a selection period in which light emission of theelectro-optic element is prepared and a light emission period in whichlight emission of the electro-optic element is performed, pieces ofprocessing of one or both of the first characteristic detection step andthe second characteristic detection step are performed only on one rowof the pixel matrix in each one frame period, and the processing of thesecond characteristic detection step is performed in the light emissionperiod.
 2. The driving method according to claim 1, wherein the piecesof processing of both the first characteristic detection step and thesecond characteristic detection step are performed only on one row ofthe pixel matrix in each one frame period, when a row on which thepieces of processing of both the first characteristic detection step andthe second characteristic detection step are performed in each frame isdefined as a monitor row and a row other than the monitor row is definedas a non-monitor row, a length of the selection period of the monitorrow is longer than a length of the selection period of the non-monitorrow, and the processing of the first characteristic detection step isperformed in the selection period.
 3. The driving method according toclaim 1, wherein the processing of one of the first characteristicdetection step and the second characteristic detection step is performedon only one row of the pixel matrix in each one frame period, whenattention is focused on one row of the pixel matrix, the processing ofthe first characteristic detection step and the processing of the secondcharacteristic detection step are alternately performed, and theprocessing of the first characteristic detection step is performed inthe light emission period.
 4. The driving method according to claim 1,wherein in the second characteristic detection step, a voltage of apositive electrode of the electro-optic element is measured in a stateof a constant current being given to the electro-optic element, todetect the characteristic of the electro-optic element.
 5. The drivingmethod according to claim 4, wherein in the second characteristicdetection step, a length of the time for giving the constant current tothe electro-optic element is adjusted in accordance with a targetluminance.
 6. The driving method according to claim 4, wherein in thesecond characteristic detection step, the constant currents at aplurality of levels are given to the electro-optic element within arange where an integrated value of a light emission current in one frameperiod becomes a value corresponding to a target gradation, to detect aplurality of characteristics as the characteristics of the electro-opticelement.
 7. The driving method according to claim 1, wherein in thesecond characteristic detection step, a current flowing in theelectro-optic element is measured in a state of a constant voltage beinggiven to the electro-optic element, to detect the characteristic of theelectro-optic element.
 8. The driving method according to claim 7,wherein in the second characteristic detection step, a length of thetime for giving the constant voltage to the electro-optic element isadjusted in accordance with a target luminance.
 9. The driving methodaccording to claim 7, wherein in the second characteristic detectionstep, the constant voltages at a plurality of levels are given to theelectro-optic element within a range where an integrated value of alight emission current in one frame period becomes a value correspondingto a target gradation, to detect a plurality of characteristics as thecharacteristics of the electro-optic element.
 10. The driving methodaccording to claim 1, wherein in the first characteristic detectionstep, a current flowing between a drain and a source of the drivetransistor is measured in a state of setting a gate-source voltage ofthe drive transistor to predetermined magnitude, to detect thecharacteristic of the drive transistor.
 11. The driving method accordingto claim 1, wherein the correction data storage portion includes anoffset value storage portion configured to store an offset value as thecorrection data, and a gain value storage portion configured to store again value as the correction data, in the correction data storage step,the sum of an offset value obtained based on the detection result in thefirst characteristic detection step and an offset value obtained basedon the detection result in the second characteristic detection step isstored as a new offset value into the offset value storage portion, andthe product of a gain value obtained based on the detection result inthe first characteristic detection step and a correction coefficientobtained based on the detection result in the second characteristicdetection step is stored as a new gain value into the gain value storageportion.
 12. The driving method according to claim 11, wherein thedisplay device further includes a characteristic detection portionconfigured to detect the characteristic of the drive transistor and thecharacteristic of the electro-optic element, and m monitor lines whichare provided so as to correspond to respective columns of the pixelmatrix and are configured so as to be made electrically connectable withthe characteristic detection portion and the pixel circuits on thecorresponding column, the selection period includes a first period inwhich the processing of the first characteristic detection step isperformed and a second period subsequent to the first period, and when avalue of a difference between the offset value stored in the offsetvalue storage portion and the offset value obtained based on thedetection result in the first characteristic detection step is definedas a first value and a value obtained based on the gain value stored inthe gain value storage portion and the gain value obtained based on thedetection result in the first characteristic detection step is definedas a second value, a voltage corresponding to the sum of the first valueand the second value is applied to each monitor line in the secondperiod.
 13. The driving method according to claim 1, wherein thecorrection data storage portion includes a drive transistor offset valuestorage portion configured to store an offset value corresponding to thedrive transistor as the correction data, an electro-optic element offsetvalue storage portion configured to store an offset value correspondingto the electro-optic element as the correction data, a drive transistorgain value storage portion configured to store a gain valuecorresponding to the drive transistor as the correction data, and anelectro-optic element gain value storage portion configured to store again value corresponding to the electro-optic element as the correctiondata, and in the correction data storage step, an offset value obtainedbased on the detection result in the first characteristic detection stepis stored as a new offset value into the drive transistor offset valuestorage portion, a gain value obtained based on the detection result inthe first characteristic detection step is stored as a new gain valueinto the drive transistor gain value storage portion, an offset valueobtained based on the detection result in the second characteristicdetection step is stored as a new offset value into the electro-opticelement offset value storage portion, and a correction coefficientobtained based on the detection result in the second characteristicdetection step is stored as a new gain value into the electro-opticelement gain value storage portion.
 14. The driving method according toclaim 13, wherein in the second characteristic detection step, a voltageof a positive electrode of the electro-optic element is measured in astate of a constant current being given to the electro-optic element, todetect the characteristic of the electro-optic element, and magnitude ofthe constant current is adjusted in accordance with the gain valuestored in the electro-optic element gain value storage portion.
 15. Thedriving method according to claim 13, wherein in the secondcharacteristic detection step, a current flowing in the electro-opticelement is measured in a state of a constant voltage being given to theelectro-optic element, to detect the characteristic of the electro-opticelement, and magnitude of the constant voltage is adjusted in accordancewith the gain value stored in the electro-optic element gain valuestorage portion.
 16. The driving method according to claim 13, whereinthe display device further includes a characteristic detection portionconfigured to detect the characteristic of the drive transistor and thecharacteristic of the electro-optic element, and m monitor lines whichare provided so as to correspond to respective columns of the pixelmatrix and are configured so as to be made electrically connectable withthe characteristic detection portion and the pixel circuits on thecorresponding column, the selection period includes a first period inwhich the processing of the first characteristic detection step isperformed and a second period subsequent to the first period, and in thesecond period, a voltage corresponding to the sum of the offset valuestored in the electro-optic element offset value storage portion and avalue obtained based on the gain value stored in the electro-opticelement gain value storage portion is applied to each monitor line. 17.The driving method according to claim 1, wherein the display devicefurther includes a characteristic detection portion which includes atleast a current measurement portion configured to measure a current anddetects the characteristic of the drive transistor and thecharacteristic of the electro-optic element, and m monitor lines whichare provided so as to correspond to respective columns of the pixelmatrix and are configured so as to be made electrically connectable withthe characteristic detection portion and the pixel circuits on thecorresponding column, and in the first characteristic detection step, acurrent flowing between a drain and a source of the drive transistor ismeasured by the current measurement portion in a state of setting agate-source voltage of the drive transistor to predetermined magnitude,in a state where the m monitor lines are electrically connected to thecorresponding pixel circuits and the current measurement portion. 18.The driving method according to claim 17, wherein the characteristicdetection portion further includes a voltage measurement portionconfigured to measure a voltage, and in the second characteristicdetection step, a voltage of a positive electrode of the electro-opticelement is measured by the voltage measurement portion in a state of aconstant current being given to the electro-optic element.
 19. Thedriving method according to claim 17, wherein in the secondcharacteristic detection step, a current flowing in the electro-opticelement is measured by the current measurement portion in a state of aconstant voltage being given to the electro-optic element.
 20. Thedriving method according to claim 17, wherein only one characteristicdetection portion is provided for each K monitor lines (K is an integernot smaller than 2 and not larger than m), and in each frame, one of theK monitor lines is electrically connected to the characteristicdetection portion, and the monitor line not electrically connected tothe characteristic detection portion is put in a high impedance state.21. The driving method according to claim 1, wherein the processing ofthe second characteristic detection step is not performed as to a pixelat which a black display or an almost black display is performed out ofthe n-row×m-column pixel matrix.
 22. The driving method according toclaim 1, further comprising a monitor region storage step of storinginformation specifying a region where the pieces of processing of one orboth of the first characteristic detection step and the secondcharacteristic detection step are last performed into a previouslyprepared monitor region storage portion during power-off of the displaydevice, wherein, after power-on of the display device, the pieces ofprocessing of one or both of the first characteristic detection step andthe second characteristic detection step are performed from a region ina vicinity of a region obtained based on the information stored in themonitor region storage portion.
 23. The driving method according toclaim 1, further comprising: a temperature detection step of detecting atemperature; and a temperature change compensation step of correctingthe characteristic data based on the temperature detected in thetemperature detection step, wherein, in the correction data storagestep, data obtained by the processing of the temperature changecompensation step is stored as the correction data into the correctiondata storage portion.
 24. The driving method according to claim 1,wherein the drive transistor is a thin-film transistor with a channellayer formed of an oxide semiconductor.
 25. The driving method accordingto claim 24, wherein the oxide semiconductor is indium gallium zincoxide mainly composed of indium (In), gallium (Ga), zinc (Zn), andoxygen (O).
 26. A display device having an n-row×m-column (n and m areintegers not smaller than 2) pixel matrix including n×m pixel circuitseach including an electro-optic element whose luminance is controlled bya current and a drive transistor configured to control a current to besupplied to the electro-optic element, the display device comprising: apixel circuit drive portion configured to drive the n×m pixel circuitswhile performing a first characteristic detection processing fordetecting a characteristic of the drive transistor and a secondcharacteristic detection processing for detecting a characteristic ofthe electro-optic element; a correction data storage portion configuredto store characteristic data obtained based on a detection result in thefirst characteristic detection processing and a detection result in thesecond characteristic detection processing as correction data forcorrecting a video signal; and a video signal correction portionconfigured to correct the video signal based on the correction datastored in the correction data storage portion, to generate a data signalto be supplied to the n×m pixel circuits, wherein one frame periodincludes a selection period in which light emission of the electro-opticelement is prepared and a light emission period in which light emissionof the electro-optic element is performed, and the pixel circuit driveportion performs one or both of the first characteristic detectionprocessing and the second characteristic detection processing for onlyone row of the pixel matrix in each one frame period, and performs thesecond characteristic detection processing in the light emission period.